1
|
Wang HC, Rauch T, Tellez-Mora A, Wirtz L, Romero AH, Marques MAL. Exploring flat-band properties in two-dimensional M 3QX 7 compounds. Phys Chem Chem Phys 2024; 26:21558-21567. [PMID: 39082370 DOI: 10.1039/d4cp01196a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/15/2024]
Abstract
We present a computational study of the M3QX7 family of two-dimensional compounds, focusing specifically on their flat-band properties. We use a high-throughput search methodology, accelerated by machine learning, to explore the vast chemical space spawned by this family. In this way, we identify numerous stable 2D compounds within the M3QX7 family. We investigate how the chemical composition can be manipulated to modulate the position and dispersion of the flat bands. By employing a tight-binding model we explain the formation of flat bands as a result of a relatively loose connection between triangular M3QX3 clusters via bridges of X atoms. The model provides an understanding of the residual interactions that can impact the band dispersion. The same loose connection between clusters not only leads to strongly localized electronic states and thus flat electronic bands but also leads to localized phonon modes and flat bands in the phonon dispersion.
Collapse
Affiliation(s)
- Hai-Chen Wang
- Research Center Future Energy Materials and Systems of the University Alliance Ruhr, Faculty of Mechanical Engineering, Ruhr University Bochum, Universitätsstraße 150, D-44801 Bochum, Germany.
| | - Tomáš Rauch
- Friedrich-Schiller-University Jena, 07743 Jena, Germany
| | - Andres Tellez-Mora
- Department of Physics, West Virginia University, Morgantown, WV 26506, USA.
| | - Ludger Wirtz
- Department of Physics and Materials Science, University of Luxembourg, 162a avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg
| | - Aldo H Romero
- Department of Physics, West Virginia University, Morgantown, WV 26506, USA.
- Department of Physics and Materials Science, University of Luxembourg, 162a avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg
| | - Miguel A L Marques
- Research Center Future Energy Materials and Systems of the University Alliance Ruhr, Faculty of Mechanical Engineering, Ruhr University Bochum, Universitätsstraße 150, D-44801 Bochum, Germany.
| |
Collapse
|
2
|
Bhowmik S, Ghosh A, Chandni U. Emergent phases in graphene flat bands. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2024; 87:096401. [PMID: 39059412 DOI: 10.1088/1361-6633/ad67ed] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 07/26/2024] [Indexed: 07/28/2024]
Abstract
Electronic correlations in two-dimensional materials play a crucial role in stabilising emergent phases of matter. The realisation of correlation-driven phenomena in graphene has remained a longstanding goal, primarily due to the absence of strong electron-electron interactions within its low-energy bands. In this context, magic-angle twisted bilayer graphene has recently emerged as a novel platform featuring correlated phases favoured by the low-energy flat bands of the underlying moiré superlattice. Notably, the observation of correlated insulators and superconductivity, and the interplay between these phases have garnered significant attention. A wealth of correlated phases with unprecedented tunability was discovered subsequently, including orbital ferromagnetism, Chern insulators, strange metallicity, density waves, and nematicity. However, a comprehensive understanding of these closely competing phases remains elusive. The ability to controllably twist and stack multiple graphene layers has enabled the creation of a whole new family of moiré superlattices with myriad properties. Here, we review the progress and development achieved so far, encompassing the rich phase diagrams offered by these graphene-based moiré systems. Additionally, we discuss multiple phases recently observed in non-moiré multilayer graphene systems. Finally, we outline future opportunities and challenges for the exploration of hidden phases in this new generation of moiré materials.
Collapse
Affiliation(s)
- Saisab Bhowmik
- Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
| | - Arindam Ghosh
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
- Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012, India
| | - U Chandni
- Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
| |
Collapse
|
3
|
Long M, Jimeno-Pozo A, Sainz-Cruz H, Pantaleón PA, Guinea F. Evolution of superconductivity in twisted graphene multilayers. Proc Natl Acad Sci U S A 2024; 121:e2405259121. [PMID: 39078673 PMCID: PMC11317599 DOI: 10.1073/pnas.2405259121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2024] [Accepted: 06/25/2024] [Indexed: 07/31/2024] Open
Abstract
The group of moiré graphene superconductors keeps growing, and by now it contains twisted graphene multilayers as well as untwisted stacks. We analyze here the contribution of long-range charge fluctuations in the superconductivity of twisted double bilayers and helical trilayers, and compare the results to twisted bilayer graphene. A diagrammatic approach which depends on a few, well-known parameters is used. We find that the critical temperature and the order parameter differ significantly between twisted double bilayers and helical trilayers on one hand, and twisted bilayer graphene on the other. This trend, consistent with experiments, can be associated with the role played by moiré Umklapp processes in the different systems.
Collapse
Affiliation(s)
- Min Long
- Instituto Madrileño de Estudios Avanzados en Nanociencia, Madrid28049, Spain
- Department of Physics, The University of Hong Kong - University of Chinese Academy of Science Joint Institute of Theoretical and Computational Physics, Hong Kong Administrative Region999077, China
| | | | - Héctor Sainz-Cruz
- Instituto Madrileño de Estudios Avanzados en Nanociencia, Madrid28049, Spain
| | - Pierre A. Pantaleón
- Instituto Madrileño de Estudios Avanzados en Nanociencia, Madrid28049, Spain
| | - Francisco Guinea
- Instituto Madrileño de Estudios Avanzados en Nanociencia, Madrid28049, Spain
- Donostia International Physics Center, San Sebastián20018, Spain
| |
Collapse
|
4
|
Chen S, Chaudhary S, Refael G, Lewandowski C. Enhancing shift current response via virtual multiband transitions. COMMUNICATIONS PHYSICS 2024; 7:250. [PMID: 39070108 PMCID: PMC11271335 DOI: 10.1038/s42005-024-01729-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2024] [Accepted: 07/02/2024] [Indexed: 07/30/2024]
Abstract
Materials exhibiting a significant shift current response could potentially outperform conventional solar cell materials. The myriad of factors governing shift-current response, however, poses significant challenges in finding such strong shift-current materials. Here we propose a general design principle that exploits inter-orbital mixing to excite virtual multiband transitions in materials with multiple flat bands to achieve an enhanced shift current response. We further relate this design principle to maximizing Wannier function spread as expressed through the formalism of quantum geometry. We demonstrate the viability of our design using a 1D stacked Rice-Mele model. Furthermore, we consider a concrete material realization - alternating angle twisted multilayer graphene (TMG) - a natural platform to experimentally realize such an effect. We identify a set of twist angles at which the shift current response is maximized via virtual transitions for each multilayer graphene and highlight the importance of TMG as a promising material to achieve an enhanced shift current response at terahertz frequencies. Our proposed mechanism also applies to other 2D systems and can serve as a guiding principle for designing multiband systems that exhibit an enhanced shift current response.
Collapse
Affiliation(s)
- Sihan Chen
- Kadanoff Center for Theoretical Physics, University of Chicago, Chicago, IL 60637 USA
- Department of Physics, California Institute of Technology, Pasadena, CA 91125 USA
| | - Swati Chaudhary
- Department of Physics, The University of Texas at Austin, Austin, TX 78712 USA
- Department of Physics, Northeastern University, Boston, MA 02115 USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
| | - Gil Refael
- Department of Physics, California Institute of Technology, Pasadena, CA 91125 USA
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA 91125 USA
| | - Cyprian Lewandowski
- National High Magnetic Field Laboratory, Tallahassee, Florida, FL 32310 USA
- Department of Physics, Florida State University, Tallahassee, FL 32306 USA
| |
Collapse
|
5
|
Hu B, Chen H, Ye Y, Huang Z, Han X, Zhao Z, Xiao H, Lin X, Yang H, Wang Z, Gao HJ. Evidence of a distinct collective mode in Kagome superconductors. Nat Commun 2024; 15:6109. [PMID: 39030195 PMCID: PMC11271580 DOI: 10.1038/s41467-024-50330-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2024] [Accepted: 07/05/2024] [Indexed: 07/21/2024] Open
Abstract
The collective modes of the superconducting order parameter fluctuation can provide key insights into the nature of the superconductor. Recently, a family of superconductors has emerged in non-magnetic kagome materials AV3Sb5 (A = K, Rb, Cs), exhibiting fertile emergent phenomenology. However, the collective behaviors of Cooper pairs have not been studied. Here, we report a distinct collective mode in CsV3-xTaxSb5 using scanning tunneling microscope/spectroscopy. The spectral line-shape is well-described by one isotropic and one anisotropic superconducting gap, and a bosonic mode due to electron-mode coupling. With increasing x, the two gaps move closer in energy, merge into two isotropic gaps of equal amplitude, and then increase synchronously. The mode energy decreases monotonically to well below 2 Δ and survives even after the charge density wave order is suppressed. We propose the interpretation of this collective mode as Leggett mode between different superconducting components or the Bardasis-Schrieffer mode due to a subleading superconducting component.
Collapse
Affiliation(s)
- Bin Hu
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Hui Chen
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
- Hefei National Laboratory, 230088, Hefei, Anhui, PR China
| | - Yuhan Ye
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Zihao Huang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Xianghe Han
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Zhen Zhao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Hongqin Xiao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Xiao Lin
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Haitao Yang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China
| | - Ziqiang Wang
- Department of Physics, Boston College, Chestnut Hill, MA, 02467, USA.
| | - Hong-Jun Gao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, PR China.
- School of Physical Sciences, University of Chinese Academy of Sciences, 100190, Beijing, PR China.
- Hefei National Laboratory, 230088, Hefei, Anhui, PR China.
| |
Collapse
|
6
|
Wang Y, Wang Z, Cao L, Han Y, Peng H, Wang Z, Xue Y, Watanabe K, Taniguchi T, Lu J, Duan J, Gao HJ, Jiang Y, Mao J. Local Gate Enhanced Correlated Phases in Twisted Monolayer-Bilayer Graphene. ACS NANO 2024; 18:17707-17714. [PMID: 38924709 DOI: 10.1021/acsnano.4c02733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/28/2024]
Abstract
Manipulating the flat band degeneracy and thus getting the correlated insulating phases has been an ideal thread for realizing the exotic quantum phenomenon in the moiré system. To achieve this goal, the delicately tuned twist angle and a substantial displacement field (D) are rigorously requested. Here, we report our scanning tunneling microscope (STM) work on reaching these correlated insulating states in twisted monolayer-bilayer graphene through a decorated tip. It acts as a local top gate, leading to an enhanced local D, and enables us to fully lift the 8-fold degeneracy of the flat bands. With the aid of this technique, we further expand the correlated insulating states into a more tolerant twist angle that is down to 0.92°. Moreover, the correlated insulating phases in the hole-doping regime are realized. Our tip decoration method allows us to integrate the STM study with the high displacement field for the correlated phases in the twisted moiré systems.
Collapse
Affiliation(s)
- Yingbo Wang
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhengwen Wang
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Lu Cao
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yingzhuo Han
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Huimin Peng
- Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100086, China
| | - Zhongrui Wang
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yucheng Xue
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Jianming Lu
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Junxi Duan
- Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100086, China
| | - Hong-Jun Gao
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Yuhang Jiang
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jinhai Mao
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| |
Collapse
|
7
|
Díaz-Reynoso UA, Huipe-Domratcheva E, Navarro O. Flat-bands in translated and twisted bilayer Penrose quasicrystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:395502. [PMID: 38906129 DOI: 10.1088/1361-648x/ad5acf] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 06/21/2024] [Indexed: 06/23/2024]
Abstract
Correlated phases in Moiré materials together with the flat-bands in twisted systems play a central role to explain superconductivity in the new twisted bilayer graphene. In this paper, flat-bands are shown to exist in both translated and twisted bilayer of quasicrystals. Such flat-bands arise for different displacements and twisting angles of two-coupled Penrose lattices where Moiré patterns are also shown. Moiré patterns analyzed in this work have at least two inverted worms showing an interference pattern going along the five-fold axes of the pentagon. In order to analyze the behavior of the flat band, our study has been done for fixed interference worm directions but increasing the worm interference density, and for fixed worm interference density but increasing the number of worm directions. In case of rotations, the Moiré patterns that occurs for special angles such asπ/5, 2π/5, 3π/5, 4π/5 andπare discussed in detail because they clearly show flat-bands along with quasicrystalline electronic states at the Fermi level.
Collapse
Affiliation(s)
- U A Díaz-Reynoso
- Unidad Morelia del Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro 8701, Colonia Ex Hacienda de San José de la Huerta, 58190 Morelia, Michoacán, Mexico
| | - E Huipe-Domratcheva
- Unidad Morelia del Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro 8701, Colonia Ex Hacienda de San José de la Huerta, 58190 Morelia, Michoacán, Mexico
| | - O Navarro
- Unidad Morelia del Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro 8701, Colonia Ex Hacienda de San José de la Huerta, 58190 Morelia, Michoacán, Mexico
| |
Collapse
|
8
|
Chen M, Xie Y, Cheng B, Yang Z, Li XZ, Chen F, Li Q, Xie J, Watanabe K, Taniguchi T, He WY, Wu M, Liang SJ, Miao F. Selective and quasi-continuous switching of ferroelectric Chern insulator devices for neuromorphic computing. NATURE NANOTECHNOLOGY 2024; 19:962-969. [PMID: 38965346 DOI: 10.1038/s41565-024-01698-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 05/19/2024] [Indexed: 07/06/2024]
Abstract
Quantum materials exhibit dissipationless topological edge state transport with quantized Hall conductance, offering notable potential for fault-tolerant computing technologies. However, the development of topological edge state-based computing devices remains a challenge. Here we report the selective and quasi-continuous ferroelectric switching of topological Chern insulator devices, showcasing a proof-of-concept demonstration in noise-immune neuromorphic computing. We fabricate this ferroelectric Chern insulator device by encapsulating magic-angle twisted bilayer graphene with doubly aligned h-BN layers and observe the coexistence of the interfacial ferroelectricity and the topological Chern insulating states. The observed ferroelectricity exhibits an anisotropic dependence on the in-plane magnetic field. By tuning the amplitude of the gate voltage pulses, we achieve ferroelectric switching between any pair of Chern insulating states in the presence of a finite magnetic field, resulting in 1,280 ferroelectric states with distinguishable Hall resistance levels on a single device. Furthermore, we demonstrate deterministic switching between two arbitrary levels among the record-high number of ferroelectric states. This unique switching capability enables the implementation of a convolutional neural network resistant to external noise, utilizing the quantized Hall conductance levels of the Chern insulator device as weights. Our study provides a promising avenue towards the development of topological quantum neuromorphic computing, where functionality and performance can be drastically enhanced by topological quantum materials.
Collapse
Affiliation(s)
- Moyu Chen
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Yongqin Xie
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Bin Cheng
- Institute of Interdisciplinary Physical Sciences, School of Science, Nanjing University of Science and Technology, Nanjing, China.
| | - Zaizheng Yang
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Xin-Zhi Li
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
| | - Fanqiang Chen
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Qiao Li
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Jiao Xie
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Wen-Yu He
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
| | - Menghao Wu
- School of Physics and School of Chemistry, Institute of Theoretical Chemistry, Huazhong University of Science and Technology, Wuhan, China
| | - Shi-Jun Liang
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
| | - Feng Miao
- Institute of Brain-Inspired Intelligence, National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
| |
Collapse
|
9
|
Li C, Xu F, Li B, Li J, Li G, Watanabe K, Taniguchi T, Tong B, Shen J, Lu L, Jia J, Wu F, Liu X, Li T. Tunable superconductivity in electron- and hole-doped Bernal bilayer graphene. Nature 2024; 631:300-306. [PMID: 38898282 DOI: 10.1038/s41586-024-07584-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 05/17/2024] [Indexed: 06/21/2024]
Abstract
Graphene-based, high-quality, two-dimensional electronic systems have emerged as a highly tunable platform for studying superconductivity1-21. Specifically, superconductivity has been observed in both electron- and hole-doped twisted graphene moiré systems1-17, whereas in crystalline graphene systems, superconductivity has so far been observed only in hole-doped rhombohedral trilayer graphene (RTG)18 and hole-doped Bernal bilayer graphene (BBG)19-21. Recently, enhanced superconductivity has been demonstrated20,21 in BBG because of the proximity to a monolayer WSe2. Here we report the observation of superconductivity and a series of flavour-symmetry-breaking phases in electron- and hole-doped BBG/WSe2 devices by electrostatic doping. The strength of the observed superconductivity is tunable by applied vertical electric fields. The maximum Berezinskii-Kosterlitz-Thouless transition temperature for the electron- and hole-doped superconductivity is about 210 mK and 400 mK, respectively. Superconductivities emerge only when the applied electric fields drive the BBG electron or hole wavefunctions towards the WSe2 layer, underscoring the importance of the WSe2 layer in the observed superconductivity. The hole-doped superconductivity violates the Pauli paramagnetic limit, consistent with an Ising-like superconductor. By contrast, the electron-doped superconductivity obeys the Pauli limit, although the proximity-induced Ising spin-orbit coupling is also notable in the conduction band. Our findings highlight the rich physics associated with the conduction band in BBG, paving the way for further studies into the superconducting mechanisms of crystalline graphene and the development of superconductor devices based on BBG.
Collapse
Affiliation(s)
- Chushan Li
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
- Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China
| | - Fan Xu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
| | - Bohao Li
- School of Physics and Technology, Wuhan University, Wuhan, China
| | - Jiayi Li
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
| | - Guoan Li
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Bingbing Tong
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Jie Shen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Li Lu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, China
- Hefei National Laboratory, Hefei, China
| | - Jinfeng Jia
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
- Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China
- Hefei National Laboratory, Hefei, China
- Shanghai Research Center for Quantum Sciences, Shanghai, China
| | - Fengcheng Wu
- School of Physics and Technology, Wuhan University, Wuhan, China.
- Wuhan Institute of Quantum Technology, Wuhan, China.
| | - Xiaoxue Liu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China.
- Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China.
- Hefei National Laboratory, Hefei, China.
- Shanghai Research Center for Quantum Sciences, Shanghai, China.
| | - Tingxin Li
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China.
- Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China.
- Hefei National Laboratory, Hefei, China.
| |
Collapse
|
10
|
Phillips J, Lado JL, Pardo V, Fumega AO. Self-doped flat band and spin-triplet superconductivity in monolayer 1T-TaSe 2-xTe x. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:385804. [PMID: 38885693 DOI: 10.1088/1361-648x/ad5946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2024] [Accepted: 06/17/2024] [Indexed: 06/20/2024]
Abstract
Two-dimensional van der Waals materials have become an established platform to engineer flat bands which can lead to strongly-correlated emergent phenomena. In particular, the family of Ta dichalcogenides in the 1T phase presents a star-of-David charge density wave that creates a flat band at the Fermi level. For TaS2and TaSe2this flat band is at half filling leading to a magnetic insulating phase. In this work, we theoretically demonstrate that ligand substitution in the TaSe2-xTexsystem produces a transition from the magnetic insulator to a non-magnetic metal in which the flat band gets doped away from half-filling. Forx∈[0.846,1.231]the spin-polarized flat band is self-doped and the system becomes a magnetic metal. In this regime, we show that attractive interactions promote three different spin-triplet superconducting phases as a function ofx, corresponding to a nodal f-wave and two topologically-different chiral p-wave superconducting phases. Our results establish monolayer TaSe2-xTexas a promising platform for correlated flat band physics leading to unconventional superconducting states.
Collapse
Affiliation(s)
- Jan Phillips
- Departamento de Física Aplicada, Universidade de Santiago de Compostela, E-15782 Campus Sur s/n, Santiago de Compostela, Spain
- Instituto de Materiais iMATUS, Universidade de Santiago de Compostela, E-15782 Campus Sur s/n, Santiago de Compostela, Spain
| | - Jose L Lado
- Department of Applied Physics, Aalto University, 02150 Espoo, Finland
| | - Víctor Pardo
- Departamento de Física Aplicada, Universidade de Santiago de Compostela, E-15782 Campus Sur s/n, Santiago de Compostela, Spain
- Instituto de Materiais iMATUS, Universidade de Santiago de Compostela, E-15782 Campus Sur s/n, Santiago de Compostela, Spain
| | - Adolfo O Fumega
- Department of Applied Physics, Aalto University, 02150 Espoo, Finland
| |
Collapse
|
11
|
Laranjeira J, Marques L, Melle-Franco M, Strutyński K. Reentrant semiconducting behavior in polymerized fullerite structures with increasing sp 3-carbon content. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:365302. [PMID: 38834086 DOI: 10.1088/1361-648x/ad540b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 06/04/2024] [Indexed: 06/06/2024]
Abstract
The electronic behavior of polymerized fullerite structures, ranging from one-dimensional to three-dimensional polymers, was studied using density functional theory with the hybrid Heyd-Scuseria-Ernzerhof functional and a 6-31G(d,p) basis set. The bandgap across these structures decreases with the rise of sp3-carbon content until metallic behavior is observed. A further increase induces a reopening of the bandgap, revealing a reentrant semiconducting behavior in this class of materials. This behavior is understood in terms of the new electronic states originated by polymeric bonding and the effect of the volume reduction on the dispersion of sp2-states. This study highlights the fullerite polymers as a magnificent platform to tune electronic properties.
Collapse
Affiliation(s)
- Jorge Laranjeira
- Departamento de Física and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
| | - Leonel Marques
- Departamento de Física and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
| | - Manuel Melle-Franco
- Departamento de Química and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
| | - Karol Strutyński
- Departamento de Química and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
| |
Collapse
|
12
|
Graf AM, Lin K, Kim M, Keski-Rahkonen J, Daza A, Heller EJ. Chaos-Assisted Dynamical Tunneling in Flat Band Superwires. ENTROPY (BASEL, SWITZERLAND) 2024; 26:492. [PMID: 38920501 PMCID: PMC11203167 DOI: 10.3390/e26060492] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2024] [Revised: 05/29/2024] [Accepted: 06/02/2024] [Indexed: 06/27/2024]
Abstract
Recent theoretical investigations have revealed unconventional transport mechanisms within high Brillouin zones of two-dimensional superlattices. Electrons can navigate along channels we call superwires, gently guided without brute force confinement. Such dynamical confinement is caused by weak superlattice deflections, markedly different from the static or energetic confinement observed in traditional wave guides or one-dimensional electron wires. The quantum properties of superwires give rise to elastic dynamical tunneling, linking disjoint regions of the corresponding classical phase space, and enabling the emergence of several parallel channels. This paper provides the underlying theory and mechanisms that facilitate dynamical tunneling assisted by chaos in periodic lattices. Moreover, we show that the mechanism of dynamical tunneling can be effectively conceptualized through the lens of a paraxial approximation. Our results further reveal that superwires predominantly exist within flat bands, emerging from eigenstates that represent linear combinations of conventional degenerate Bloch states. Finally, we quantify tunneling rates across various lattice configurations and demonstrate that tunneling can be suppressed in a controlled fashion, illustrating potential implications in future nanodevices.
Collapse
Affiliation(s)
- Anton M. Graf
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA;
- Department of Physics, Harvard University, Cambridge, MA 02138, USA; (K.L.); (M.K.); (J.K.-R.); (A.D.)
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| | - Ke Lin
- Department of Physics, Harvard University, Cambridge, MA 02138, USA; (K.L.); (M.K.); (J.K.-R.); (A.D.)
- Zhiyuan College, Shanghai Jiao Tong University, Shanghai 200240, China
| | - MyeongSeo Kim
- Department of Physics, Harvard University, Cambridge, MA 02138, USA; (K.L.); (M.K.); (J.K.-R.); (A.D.)
- Harvard College, Harvard University, Cambridge, MA 02138, USA
| | - Joonas Keski-Rahkonen
- Department of Physics, Harvard University, Cambridge, MA 02138, USA; (K.L.); (M.K.); (J.K.-R.); (A.D.)
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| | - Alvar Daza
- Department of Physics, Harvard University, Cambridge, MA 02138, USA; (K.L.); (M.K.); (J.K.-R.); (A.D.)
- Nonlinear Dynamics, Chaos and Complex Systems Group, Departamento de Física, Universidad Rey Juan Carlos, Tulipán s/n, 28933 Mostoles, Madrid, Spain
| | - Eric J. Heller
- Department of Physics, Harvard University, Cambridge, MA 02138, USA; (K.L.); (M.K.); (J.K.-R.); (A.D.)
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
| |
Collapse
|
13
|
Que ZX, Li SZ, Huang B, Yang ZX, Zhang WB. Ultra-flat bands at large twist angles in group-V twisted bilayer materials. J Chem Phys 2024; 160:194710. [PMID: 38767261 DOI: 10.1063/5.0197757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 05/01/2024] [Indexed: 05/22/2024] Open
Abstract
Flat bands in 2D twisted materials are key to the realization of correlation-related exotic phenomena. However, a flat band often was achieved in the large system with a very small twist angle, which enormously increases the computational and experimental complexity. In this work, we proposed group-V twisted bilayer materials, including P, As, and Sb in the β phase with large twist angles. The band structure of twisted bilayer materials up to 2524 atoms has been investigated by a deep learning method DeepH, which significantly reduces the computational time. Our results show that the bandgap and the flat bandwidth of twisted bilayer β-P, β-As, and β-Sb reduce gradually with the decreasing of twist angle, and the ultra-flat band with bandwidth approaching 0 eV is achieved. Interestingly, we found that a twist angle of 9.43° is sufficient to achieve the band flatness for β-As comparable to that of twist bilayer graphene at the magic angle of 1.08°. Moreover, we also find that the bandgap reduces with decreasing interlayer distance while the flat band is still preserved, which suggests interlayer distance as an effective routine to tune the bandgap of flat band systems. Our research provides a feasible platform for exploring physical phenomena related to flat bands in twisted layered 2D materials.
Collapse
Affiliation(s)
- Zhi-Xiong Que
- Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, China
| | - Shu-Zong Li
- Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, China
| | - Bo Huang
- Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, China
| | - Zhi-Xiong Yang
- Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, China
| | - Wei-Bing Zhang
- Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, China
| |
Collapse
|
14
|
Zhu X, Sun J, Feng S, Guo H. Moiré band renormalization due to lattice mismatch in bilayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:315502. [PMID: 38663420 DOI: 10.1088/1361-648x/ad43a3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Accepted: 04/25/2024] [Indexed: 05/08/2024]
Abstract
We investigated the band renormalization caused by the compressive-strain-induced lattice mismatch in parallel AA stacked bilayer graphene using two complementary methods: the tight-binding approach and the low-energy continuum theory. While a large mismatch does not alter the low-energy bands, a small one reduces the bandwidth of the low-energy bands along with a decrease in the Fermi velocity. In the tiny-mismatch regime, the low-energy continuum theory reveals that the long-period moiré pattern extensively renormalizes the low-energy bands, resulting in a significant reduction of bandwidth. Meanwhile, the Fermi velocity exhibits an oscillatory behavior and approaches zero at specific mismatches. However, the resulting low-energy bands are not perfectly isolated flat, as seen in twisted bilayer graphene at magic angles. These findings provide a deeper understanding of moiré physics and offer valuable guidance for related experimental studies in creating moiré superlattices using two-dimensional van der Waals heterostructures.
Collapse
Affiliation(s)
- Xingchuan Zhu
- Interdisciplinary Center for Fundamental and Frontier Sciences, Nanjing University of Science and Technology, Jiangyin, Jiangsu 214443, People's Republic of China
| | - Junsong Sun
- School of Physics, Beihang University, Beijing 100191, People's Republic of China
| | - Shiping Feng
- Department of Physics, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Huaiming Guo
- School of Physics, Beihang University, Beijing 100191, People's Republic of China
| |
Collapse
|
15
|
Li H, Xiang Z, Naik MH, Kim W, Li Z, Sailus R, Banerjee R, Taniguchi T, Watanabe K, Tongay S, Zettl A, da Jornada FH, Louie SG, Crommie MF, Wang F. Imaging moiré excited states with photocurrent tunnelling microscopy. NATURE MATERIALS 2024; 23:633-638. [PMID: 38172545 DOI: 10.1038/s41563-023-01753-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 11/06/2023] [Indexed: 01/05/2024]
Abstract
Moiré superlattices provide a highly tuneable and versatile platform to explore novel quantum phases and exotic excited states ranging from correlated insulators to moiré excitons. Scanning tunnelling microscopy has played a key role in probing microscopic behaviours of the moiré correlated ground states at the atomic scale. However, imaging of quantum excited states in moiré heterostructures remains an outstanding challenge. Here we develop a photocurrent tunnelling microscopy technique that combines laser excitation and scanning tunnelling spectroscopy to directly visualize the electron and hole distribution within the photoexcited moiré exciton in twisted bilayer WS2. The tunnelling photocurrent alternates between positive and negative polarities at different locations within a single moiré unit cell. This alternating photocurrent originates from the in-plane charge transfer moiré exciton in twisted bilayer WS2, predicted by our GW-Bethe-Salpeter equation calculations, that emerges from the competition between the electron-hole Coulomb interaction and the moiré potential landscape. Our technique enables the exploration of photoexcited non-equilibrium moiré phenomena at the atomic scale.
Collapse
Affiliation(s)
- Hongyuan Li
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
- Graduate Group in Applied Science and Technology, University of California Berkeley, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Ziyu Xiang
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
- Graduate Group in Applied Science and Technology, University of California Berkeley, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Mit H Naik
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Woochang Kim
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Zhenglu Li
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Renee Sailus
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Rounak Banerjee
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Sefaattin Tongay
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Alex Zettl
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- Kavli Energy Nano Sciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Felipe H da Jornada
- Department of Materials Science and Engineering, Stanford University, Palo Alto, CA, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Steven G Louie
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
| | - Michael F Crommie
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
- Kavli Energy Nano Sciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
| | - Feng Wang
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
- Kavli Energy Nano Sciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
| |
Collapse
|
16
|
Tian H, Tu T, Jin X, Li C, Lin T, Dong Q, Jing X, Liu B, Liu R, Li D, Liu Z, Li Q, Peng H, Liu B. Tuning the Flat Band in Bi 2O 2Se by Pressure to Induce Superconductivity. J Am Chem Soc 2024; 146:7324-7331. [PMID: 38445458 DOI: 10.1021/jacs.3c11984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
The discovery of superconductivity in twisted bilayer graphene has reignited enthusiasm in the field of flat-band superconductivity. However, important challenges remain, such as constructing a flat-band structure and inducing a superconducting state in materials. Here, we successfully achieved superconductivity in Bi2O2Se by pressure-tuning the flat-band electronic structure. Experimental measurements combined with theoretical calculations reveal that the occurrence of pressure-induced superconductivity at 30 GPa is associated with a flat-band electronic structure near the Fermi level. Moreover, in Bi2O2Se, a van Hove singularity is observed at the Fermi level alongside pronounced Fermi surface nesting. These remarkable features play a crucial role in promoting strong electron-phonon interactions, thus potentially enhancing the superconducting properties of the material. These findings demonstrate that pressure offers a potential experimental strategy for precisely tuning the flat band and achieving superconductivity.
Collapse
Affiliation(s)
- Hui Tian
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
- School of Science, Shenyang Ligong University, Shenyang 110158, China
| | - Teng Tu
- Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Xilian Jin
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Chenyi Li
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Tao Lin
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Qing Dong
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Xiaoling Jing
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Bo Liu
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Ran Liu
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Da Li
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Zhongkai Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Quanjun Li
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Hailin Peng
- Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Bingbing Liu
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| |
Collapse
|
17
|
Li K, Yin LJ, Che C, Zhang S, Liu X, Xiao Y, Liu S, Tong Q, Li SY, Pan A. Correlation-Induced Symmetry-Broken States in Large-Angle Twisted Bilayer Graphene on MoS 2. ACS NANO 2024; 18:7937-7944. [PMID: 38441035 DOI: 10.1021/acsnano.3c09993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/06/2024]
Abstract
Strongly correlated states commonly emerge in twisted bilayer graphene (TBG) with "magic-angle" (1.1°), where the electron-electron (e-e) interaction U becomes prominent relative to the small bandwidth W of the nearly flat band. However, the stringent requirement of this magic angle makes the sample preparation and the further application facing great challenges. Here, using scanning tunneling microscopy (STM) and spectroscopy (STS), we demonstrate that the correlation-induced symmetry-broken states can also be achieved in a 3.45° TBG, via engineering this nonmagic-angle TBG into regimes of U/W > 1. We enhance the e-e interaction through controlling the microscopic dielectric environment by using a MoS2 substrate. Simultaneously, the width of the low-energy van Hove singularity (VHS) peak is reduced by enhancing the interlayer coupling via STM tip modulation. When partially filled, the VHS peak exhibits a giant splitting into two states flanked by the Fermi level and shows a symmetry-broken LDOS distribution with a stripy charge order, which confirms the existence of strong correlation effect in our 3.45° TBG. Our result demonstrates the feasibility of the study and application of the correlation physics in TBGs with a wider range of twist angle.
Collapse
Affiliation(s)
- Kaihui Li
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
| | - Long-Jing Yin
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Chenglong Che
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Shihao Zhang
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Xueying Liu
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
| | - Yulong Xiao
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
| | - Songlong Liu
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Qingjun Tong
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Si-Yu Li
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
- Greater Bay Area Institute for Innovation, Hunan University, Guangzhou 511300, People's Republic of China
| | - Anlian Pan
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
- School of Physics and Electronics, Hunan Normal University, Changsha 410081, People's Republic of China
| |
Collapse
|
18
|
Wang J, Cheng F, Sun Y, Xu H, Cao L. Stacking engineering in layered homostructures: transitioning from 2D to 3D architectures. Phys Chem Chem Phys 2024; 26:7988-8012. [PMID: 38380525 DOI: 10.1039/d3cp04656g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2024]
Abstract
Artificial materials, characterized by their distinctive properties and customized functionalities, occupy a central role in a wide range of applications including electronics, spintronics, optoelectronics, catalysis, and energy storage. The emergence of atomically thin two-dimensional (2D) materials has driven the creation of artificial heterostructures, harnessing the potential of combining various 2D building blocks with complementary properties through the art of stacking engineering. The promising outcomes achieved for heterostructures have spurred an inquisitive exploration of homostructures, where identical 2D layers are precisely stacked. This perspective primarily focuses on the field of stacking engineering within layered homostructures, where precise control over translational or rotational degrees of freedom between vertically stacked planes or layers is paramount. In particular, we provide an overview of recent advancements in the stacking engineering applied to 2D homostructures. Additionally, we will shed light on research endeavors venturing into three-dimensional (3D) structures, which allow us to proactively address the limitations associated with artificial 2D homostructures. We anticipate that the breakthroughs in stacking engineering in 3D materials will provide valuable insights into the mechanisms governing stacking effects. Such advancements have the potential to unlock the full capability of artificial layered homostructures, propelling the future development of materials, physics, and device applications.
Collapse
Affiliation(s)
- Jiamin Wang
- Changchun Institute of Optics, Fine Mechanics & Physics (CIOMP), Chinese Academy of Sciences, Changchun 130033, P. R. China.
- University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Fang Cheng
- State Key Laboratory for Organic Electronics and Information Displays & Jiangsu Key Laboratory for Biosensors, Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts and Telecommunications, Nanjing 210023, P. R. China
| | - Yan Sun
- Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, P. R. China.
| | - Hai Xu
- Changchun Institute of Optics, Fine Mechanics & Physics (CIOMP), Chinese Academy of Sciences, Changchun 130033, P. R. China.
- University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, P. R. China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Liang Cao
- Anhui Key Laboratory of Low-Energy Quantum Materials and Devices, High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences, Hefei 230031, P. R. China.
| |
Collapse
|
19
|
Sun X, Suriyage M, Khan AR, Gao M, Zhao J, Liu B, Hasan MM, Rahman S, Chen RS, Lam PK, Lu Y. Twisted van der Waals Quantum Materials: Fundamentals, Tunability, and Applications. Chem Rev 2024; 124:1992-2079. [PMID: 38335114 DOI: 10.1021/acs.chemrev.3c00627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2024]
Abstract
Twisted van der Waals (vdW) quantum materials have emerged as a rapidly developing field of two-dimensional (2D) semiconductors. These materials establish a new central research area and provide a promising platform for studying quantum phenomena and investigating the engineering of novel optoelectronic properties such as single photon emission, nonlinear optical response, magnon physics, and topological superconductivity. These captivating electronic and optical properties result from, and can be tailored by, the interlayer coupling using moiré patterns formed by vertically stacking atomic layers with controlled angle misorientation or lattice mismatch. Their outstanding properties and the high degree of tunability position them as compelling building blocks for both compact quantum-enabled devices and classical optoelectronics. This paper offers a comprehensive review of recent advancements in the understanding and manipulation of twisted van der Waals structures and presents a survey of the state-of-the-art research on moiré superlattices, encompassing interdisciplinary interests. It delves into fundamental theories, synthesis and fabrication, and visualization techniques, and the wide range of novel physical phenomena exhibited by these structures, with a focus on their potential for practical device integration in applications ranging from quantum information to biosensors, and including classical optoelectronics such as modulators, light emitting diodes, lasers, and photodetectors. It highlights the unique ability of moiré superlattices to connect multiple disciplines, covering chemistry, electronics, optics, photonics, magnetism, topological and quantum physics. This comprehensive review provides a valuable resource for researchers interested in moiré superlattices, shedding light on their fundamental characteristics and their potential for transformative applications in various fields.
Collapse
Affiliation(s)
- Xueqian Sun
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Manuka Suriyage
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Ahmed Raza Khan
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Department of Industrial and Manufacturing Engineering, University of Engineering and Technology (Rachna College Campus), Gujranwala, Lahore 54700, Pakistan
| | - Mingyuan Gao
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- College of Engineering and Technology, Southwest University, Chongqing 400716, China
| | - Jie Zhao
- Department of Quantum Science & Technology, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Boqing Liu
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Md Mehedi Hasan
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Sharidya Rahman
- Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia
- ARC Centre of Excellence in Exciton Science, Monash University, Clayton, Victoria 3800, Australia
| | - Ruo-Si Chen
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Ping Koy Lam
- Department of Quantum Science & Technology, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Yuerui Lu
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| |
Collapse
|
20
|
Poduval PP, Scheurer MS. Vestigial singlet pairing in a fluctuating magnetic triplet superconductor and its implications for graphene superlattices. Nat Commun 2024; 15:1713. [PMID: 38402211 PMCID: PMC10894192 DOI: 10.1038/s41467-024-45950-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 02/08/2024] [Indexed: 02/26/2024] Open
Abstract
Stacking and twisting graphene layers allows to create and control a two-dimensional electron liquid with strong correlations. Experiments indicate that these systems exhibit strong tendencies towards both magnetism and triplet superconductivity. Motivated by this phenomenology, we study a 2D model of fluctuating triplet pairing and spin magnetism. Individually, their respective order parameters, d and N, cannot order at finite temperature. Nonetheless, the model exhibits a variety of vestigial phases, including charge-4e superconductivity and broken time-reversal symmetry. Our main focus is on a phase characterized by finite d ⋅ N, which has the same symmetries as the BCS state, a Meissner effect, and metastable supercurrents, yet rather different spectral properties: most notably, the suppression of the electronic density of states at the Fermi level can resemble that of either a fully gapped or nodal superconductor, depending on parameters. This provides a possible explanation for recent tunneling experiments in the superconducting phase of graphene moiré systems.
Collapse
Affiliation(s)
- Prathyush P Poduval
- Donald Bren School of Information and Computer Sciences, University of California, Irvine, CA, 92697, USA.
- Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, MD, 20742, USA.
| | - Mathias S Scheurer
- Institute for Theoretical Physics III, University of Stuttgart, 70550, Stuttgart, Germany.
- Institute for Theoretical Physics, University of Innsbruck, Innsbruck, A-6020, Austria.
| |
Collapse
|
21
|
Kuang X, Pantaleón Peralta PA, Angel Silva-Guillén J, Yuan S, Guinea F, Zhan Z. Optical properties and plasmons in moiré structures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:173001. [PMID: 38232397 DOI: 10.1088/1361-648x/ad1f8c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Accepted: 01/17/2024] [Indexed: 01/19/2024]
Abstract
The discoveries of numerous exciting phenomena in twisted bilayer graphene (TBG) are stimulating significant investigations on moiré structures that possess a tunable moiré potential. Optical response can provide insights into the electronic structures and transport phenomena of non-twisted and twisted moiré structures. In this article, we review both experimental and theoretical studies of optical properties such as optical conductivity, dielectric function, non-linear optical response, and plasmons in moiré structures composed of graphene, hexagonal boron nitride (hBN), and/or transition metal dichalcogenides. Firstly, a comprehensive introduction to the widely employed methodology on optical properties is presented. After, moiré potential induced optical conductivity and plasmons in non-twisted structures are reviewed, such as single layer graphene-hBN, bilayer graphene-hBN and graphene-metal moiré heterostructures. Next, recent investigations of twist-angle dependent optical response and plasmons are addressed in twisted moiré structures. Additionally, we discuss how optical properties and plasmons could contribute to the understanding of the many-body effects and superconductivity observed in moiré structures.
Collapse
Affiliation(s)
- Xueheng Kuang
- Yangtze Delta Industrial Innovation Center of Quantum Science and Technology, Suzhou 215000, People's Republic of China
| | | | - Jose Angel Silva-Guillén
- Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
| | - Shengjun Yuan
- Key Laboratory of Artificial Micro- and Nano-structures of the Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, People's Republic of China
- Wuhan Institute of Quantum Technology, Wuhan 430206, People's Republic of China
| | - Francisco Guinea
- Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
- Donostia International Physics Center, Paseo Manuel de Lardizábal 4, 20018 San Sebastián, Spain
| | - Zhen Zhan
- Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
| |
Collapse
|
22
|
Mu Z, Zhang Y, An J, Zhang X, Zhou H, Song H, He C, Liu G, Cheng C. Manipulating the Generation of Photonic Moiré Lattices Using Plasmonic Metasurfaces. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:230. [PMID: 38276748 PMCID: PMC11154393 DOI: 10.3390/nano14020230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 01/18/2024] [Accepted: 01/19/2024] [Indexed: 01/27/2024]
Abstract
The generation of moiré lattices by superimposing two identical sublattices at a specific twist angle has garnered significant attention owing to its potential applications, ranging from two-dimensional materials to manipulating light propagation. While macroscale moiré lattices have been widely studied, further developments in manipulating moiré lattices at the subwavelength scale would be crucial for miniaturizing and integrating platforms. Here, we propose a plasmonic metasurface design consisting of rotated nanoslits arranged within N + N' round apertures for generating focused moiré lattices. By introducing a spin-dependent geometric phase through the rotated nanoslits, an overall lens and spiral phase can be achieved, allowing each individual set of round apertures to generate a periodic lattice in the focal plane. Superimposing two sets of N and N' apertures at specific twist angles and varying phase differences allows for the superposition of two sublattices with different periods, leading to the formation of diverse moiré patterns. Our simulations and theoretical results demonstrate the feasibility of our proposed metasurface design. Due to their compactness and tunability, the utilization of metasurfaces in creating nanoscale photonic moiré lattices is anticipated to find extensive applications in integrated and on-chip optical systems.
Collapse
Affiliation(s)
- Zhanliang Mu
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Yuqin Zhang
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Jianshan An
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Xuehui Zhang
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Haoran Zhou
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Hongsheng Song
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Changwei He
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Guiyuan Liu
- School of Science, Shandong Jianzhu University, Jinan 250101, China; (Z.M.); (J.A.); (X.Z.); (H.Z.); (H.S.); (C.H.); (G.L.)
| | - Chuanfu Cheng
- College of Physics and Electronics, Shandong Normal University, Jinan 250014, China;
| |
Collapse
|
23
|
Shayeganfar F, Ramazani A, Habibiyan H, Rafiee Diznab M. Terahertz linear/non-linear anomalous Hall conductivity of moiré TMD hetero-nanoribbons as topological valleytronics materials. Sci Rep 2024; 14:1581. [PMID: 38238394 PMCID: PMC10796390 DOI: 10.1038/s41598-024-51721-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Accepted: 01/09/2024] [Indexed: 01/22/2024] Open
Abstract
Twisted moiré van der Waals heterostructures hold promise to provide a robust quantum simulation platform for strongly correlated materials and realize elusive states of matter such as topological states in the laboratory. We demonstrated that the moiré bands of twisted transition metal dichalcogenide (TMD) hetero-nanoribbons exhibit non-trivial topological order due to the tendency of valence and conduction band states in K valleys to form giant band gaps when spin-orbit coupling (SOC) is taken into account. Among the features of twisted WS[Formula: see text]/MoS[Formula: see text] and WSe[Formula: see text]/MoSe[Formula: see text], we found that the heavy fermions associated with the topological flat bands and the presence of strongly correlated states, enhance anomalous Hall conductivity (AHC) away from the magic angle. By band analysis, we showed that the topmost conduction bands from the ± K-valleys are perfectly flat and carry a spin/valley Chern number. Moreover, we showed that the non-linear anomalous Hall effect in moiré TMD hetero-nanoribbons can be used to manipulate terahertz (THz) radiation. Our findings establish twisted heterostructures of group-VI TMD nanoribbons as a tunable platform for engineering topological valley quantum phases and THz non-linear Hall conductivity.
Collapse
Affiliation(s)
- Farzaneh Shayeganfar
- Department of Physics and Energy Engineering, Amirkabir University of Technology, Tehran, Iran.
| | - Ali Ramazani
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Hamidreza Habibiyan
- Department of Physics and Energy Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Mohammad Rafiee Diznab
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| |
Collapse
|
24
|
Li Y, Zhang F, Ha VA, Lin YC, Dong C, Gao Q, Liu Z, Liu X, Ryu SH, Kim H, Jozwiak C, Bostwick A, Watanabe K, Taniguchi T, Kousa B, Li X, Rotenberg E, Khalaf E, Robinson JA, Giustino F, Shih CK. Tuning commensurability in twisted van der Waals bilayers. Nature 2024; 625:494-499. [PMID: 38233619 DOI: 10.1038/s41586-023-06904-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Accepted: 11/28/2023] [Indexed: 01/19/2024]
Abstract
Moiré superlattices based on van der Waals bilayers1-4 created at small twist angles lead to a long wavelength pattern with approximate translational symmetry. At large twist angles (θt), moiré patterns are, in general, incommensurate except for a few discrete angles. Here we show that large-angle twisted bilayers offer distinctly different platforms. More specifically, by using twisted tungsten diselenide bilayers, we create the incommensurate dodecagon quasicrystals at θt = 30° and the commensurate moiré crystals at θt = 21.8° and 38.2°. Valley-resolved scanning tunnelling spectroscopy shows disparate behaviours between moiré crystals (with translational symmetry) and quasicrystals (with broken translational symmetry). In particular, the K valley shows rich electronic structures exemplified by the formation of mini-gaps near the valence band maximum. These discoveries demonstrate that bilayers with large twist angles offer a design platform to explore moiré physics beyond those formed with small twist angles.
Collapse
Affiliation(s)
- Yanxing Li
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Fan Zhang
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Viet-Anh Ha
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
- Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, USA
| | - Yu-Chuan Lin
- Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA, USA
- Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
| | - Chengye Dong
- Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA, USA
| | - Qiang Gao
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Zhida Liu
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Xiaohui Liu
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Sae Hee Ryu
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Hyunsue Kim
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Chris Jozwiak
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Aaron Bostwick
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Kenji Watanabe
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Bishoy Kousa
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Xiaoqin Li
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Eli Rotenberg
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Eslam Khalaf
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Joshua A Robinson
- Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA, USA
| | - Feliciano Giustino
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
- Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, USA
| | - Chih-Kang Shih
- Department of Physics, The University of Texas at Austin, Austin, TX, USA.
| |
Collapse
|
25
|
Samanta S, Hong D, Kim HS. Electronic Structures of Kitaev Magnet Candidates RuCl 3 and RuI 3. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 14:9. [PMID: 38202464 PMCID: PMC10780606 DOI: 10.3390/nano14010009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 12/13/2023] [Accepted: 12/18/2023] [Indexed: 01/12/2024]
Abstract
Layered honeycomb magnets with strong atomic spin-orbit coupling at transition metal sites have been intensively studied for the search of Kitaev magnetism and the resulting non-Abelian braiding statistics. α-RuCl3 has been the most promising candidate, and there have been several reports on the realization of sibling compounds α-RuBr3 and α-RuI3 with the same crystal structure. Here, we investigate correlated electronic structures of α-RuCl3 and α-RuI3 by employing first-principles dynamical mean-field theory. Our result provides a valuable insight into the discrepancy between experimental and theoretical reports on transport properties of α-RuI3, and suggests a potential realization of correlated flat bands with strong spin-orbit coupling and a quantum spin-Hall insulating phase in α-RuI3.
Collapse
Affiliation(s)
- Subhasis Samanta
- Department of Physics, Kangwon National University, Chuncheon 24341, Republic of Korea; (S.S.); (D.H.)
| | - Dukgeun Hong
- Department of Physics, Kangwon National University, Chuncheon 24341, Republic of Korea; (S.S.); (D.H.)
| | - Heung-Sik Kim
- Department of Physics, Kangwon National University, Chuncheon 24341, Republic of Korea; (S.S.); (D.H.)
- Institute of Quantum Convergence and Technology, Kangwon National University, Chuncheon 24341, Republic of Korea
| |
Collapse
|
26
|
Christos M, Sachdev S, Scheurer MS. Nodal band-off-diagonal superconductivity in twisted graphene superlattices. Nat Commun 2023; 14:7134. [PMID: 37932262 PMCID: PMC10628137 DOI: 10.1038/s41467-023-42471-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 10/11/2023] [Indexed: 11/08/2023] Open
Abstract
The superconducting state and mechanism are among the least understood phenomena in twisted graphene systems. Recent tunneling experiments indicate a transition between nodal and gapped pairing with electron filling, which is not naturally understood within current theory. We demonstrate that the coexistence of superconductivity and flavor polarization leads to pairing channels that are guaranteed by symmetry to be entirely band-off-diagonal, with a variety of consequences: most notably, the pairing invariant under all symmetries can have Bogoliubov Fermi surfaces in the superconducting state with protected nodal lines, or may be fully gapped, depending on parameters, and the band-off-diagonal chiral p-wave state exhibits transitions between gapped and nodal regions upon varying the doping. We demonstrate that band-off-diagonal pairing can be the leading state when only phonons are considered, and is also uniquely favored by fluctuations of a time-reversal-symmetric intervalley coherent order motivated by recent experiments. Consequently, band-off-diagonal superconductivity allows for the reconciliation of several key experimental observations in graphene moiré systems.
Collapse
Affiliation(s)
- Maine Christos
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
| | - Subir Sachdev
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
| | - Mathias S Scheurer
- Institute for Theoretical Physics, University of Innsbruck, Innsbruck, A-6020, Austria.
- Institute for Theoretical Physics III, University of Stuttgart, 70550, Stuttgart, Germany.
| |
Collapse
|
27
|
Vaňo V, Ganguli SC, Amini M, Yan L, Khosravian M, Chen G, Kezilebieke S, Lado JL, Liljeroth P. Evidence of Nodal Superconductivity in Monolayer 1H-TaS 2 with Hidden Order Fluctuations. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2305409. [PMID: 37592888 DOI: 10.1002/adma.202305409] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 08/07/2023] [Indexed: 08/19/2023]
Abstract
Unconventional superconductors represent one of the fundamental directions in modern quantum materials research. In particular, nodal superconductors are known to appear naturally in strongly correlated systems, including cuprate superconductors and heavy-fermion systems. Van der Waals materials hosting superconducting states are well known, yet nodal monolayer van der Waals superconductors have remained elusive. Here, using low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments, it is shown that pristine monolayer 1H-TaS2 realizes a nodal superconducting state. Non-magnetic disorder drives the nodal superconducting state to a conventional gapped s-wave state. Furthermore, many-body excitations emerge close to the gap edge, signalling a potential unconventional pairing mechanism. The results demonstrate the emergence of nodal superconductivity in a van der Waals monolayer, providing a building block for van der Waals heterostructures exploiting unconventional superconducting states.
Collapse
Affiliation(s)
- Viliam Vaňo
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| | | | - Mohammad Amini
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| | - Linghao Yan
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, Jiangsu, 215123, P. R. China
| | - Maryam Khosravian
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| | - Guangze Chen
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
- Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, 41296, Sweden
| | - Shawulienu Kezilebieke
- Department of Physics, Department of Chemistry and Nanoscience Center, University of Jyväskylä, University of Jyväskylä, FI-40014, Finland
| | - Jose L Lado
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| | - Peter Liljeroth
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| |
Collapse
|
28
|
Xie YM, Lantagne-Hurtubise É, Young AF, Nadj-Perge S, Alicea J. Gate-Defined Topological Josephson Junctions in Bernal Bilayer Graphene. PHYSICAL REVIEW LETTERS 2023; 131:146601. [PMID: 37862641 DOI: 10.1103/physrevlett.131.146601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 09/07/2023] [Indexed: 10/22/2023]
Abstract
Recent experiments on Bernal bilayer graphene (BLG) deposited on monolayer WSe_{2} revealed robust, ultraclean superconductivity coexisting with sizable induced spin-orbit coupling. Here, we propose BLG/WSe_{2} as a platform to engineer gate-defined planar topological Josephson junctions, where the normal and superconducting regions descend from a common material. More precisely, we show that if superconductivity in BLG/WSe_{2} is gapped and emerges from a parent state with intervalley coherence, then Majorana zero-energy modes can form in the barrier region upon applying weak in-plane magnetic fields. Our results spotlight a potential pathway for "internally engineered" topological superconductivity that minimizes detrimental disorder and orbital-magnetic-field effects.
Collapse
Affiliation(s)
- Ying-Ming Xie
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
| | - Étienne Lantagne-Hurtubise
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
| | - Andrea F Young
- Department of Physics, University of California at Santa Barbara, Santa Barbara, California 93106, USA
| | - Stevan Nadj-Perge
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
- T. J. Watson Laboratory of Applied Physics, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA
| | - Jason Alicea
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
| |
Collapse
|
29
|
Yin R, Wang Z, Tan S, Ma C, Wang B. On-Surface Synthesis of Graphene Nanoribbons with Atomically Precise Structural Heterogeneities and On-Site Characterizations. ACS NANO 2023; 17:17610-17623. [PMID: 37666005 DOI: 10.1021/acsnano.3c06128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/06/2023]
Abstract
Graphene nanoribbons (GNRs) are strips of graphene, with widths of a few nanometers, that are promising candidates for future applications in nanodevices and quantum information processing due to their highly tunable structure-dependent electronic, spintronic, topological, and optical properties. Implantation of periodic structural heterogeneities, such as heteroatoms, nanopores, and non-hexagonal rings, has become a powerful manner for tailoring the designer properties of GNRs. The bottom-up synthesis approach, by combining on-surface chemical reactions based on rationally designed molecular precursors and in situ tip-based microscopic and spectroscopic techniques, promotes the construction of atomically precise GNRs with periodic structural modulations. However, there are still obstacles and challenges lying on the way toward the understanding of the intrinsic structure-property relations, such as the strong screening and Fermi level pinning effect of the normally used transition metal substrates and the lack of collective tip-based techniques that can cover multi-internal degrees of freedom of the GNRs. In this Perspective, we briefly review the recent progress in the on-surface synthesis of GNRs with diverse structural heterogeneities and highlight the structure-property relations as characterized by the noncontact atomic force microscopy and scanning tunneling microscopy/spectroscopy. We furthermore motivate to deliver the need for developing strategies to achieve quasi-freestanding GNRs and for exploiting multifunctional tip-based techniques to collectively probe the intrinsic properties.
Collapse
Affiliation(s)
- Ruoting Yin
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Zhengya Wang
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Shijing Tan
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Chuanxu Ma
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Bing Wang
- Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information & Quantum Physics, New Cornerstone Science Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| |
Collapse
|
30
|
Liu M, Senga R, Koshino M, Lin YC, Suenaga K. Direct Observation of Locally Modified Excitonic Effects within a Moiré Unit Cell in Twisted Bilayer Graphene. ACS NANO 2023; 17:18433-18440. [PMID: 37682623 DOI: 10.1021/acsnano.3c06021] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/10/2023]
Abstract
Bilayer graphene, which forms moiré superlattices, possesses distinct electronic and optical properties owing to its hybridized energy band and the emergence of van Hove singularities depending on its twist angle. Extensive research has been conducted on the global characteristics of moiré superlattices induced by their long-range periodicity. However, the local properties, which differ owing to the variations in the three-dimensional atomic arrangement, within a moiré unit cell have been rarely explored. In this study, we demonstrate the highly localized excitation of carbon 1s electrons to unoccupied van Hove singularities in twisted bilayer graphene by electron energy loss spectroscopy using a monochromated transmission electron microscope. The core-level excitations associated with the van Hove singularities exhibit a systematic twist-angle dependence analogous to optical excitations. Furthermore, local variations in the core-level van Hove singularity peaks, which can originate from the core-exciton lifetimes and band modifications corresponding to the local stacking geometry within a moiré unit cell, are unambiguously corroborated.
Collapse
Affiliation(s)
- Ming Liu
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| | - Ryosuke Senga
- Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8565, Japan
| | - Masanori Koshino
- Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8565, Japan
| | - Yung-Chang Lin
- Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8565, Japan
| | - Kazu Suenaga
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
| |
Collapse
|
31
|
Li Y, Wan Q, Xu N. Recent Advances in Moiré Superlattice Systems by Angle-Resolved Photoemission Spectroscopy. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023:e2305175. [PMID: 37689836 DOI: 10.1002/adma.202305175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 08/16/2023] [Indexed: 09/11/2023]
Abstract
The last decade has witnessed a flourish in 2D materials including graphene and transition metal dichalcogenides (TMDs) as atomic-scale Legos. Artificial moiré superlattices via stacking 2D materials with a twist angle and/or a lattice mismatch have recently become a fertile playground exhibiting a plethora of emergent properties beyond their building blocks. These rich quantum phenomena stem from their nontrivial electronic structures that are effectively tuned by the moiré periodicity. Modern angle-resolved photoemission spectroscopy (ARPES) can directly visualize electronic structures with decent momentum, energy, and spatial resolution, thus can provide enlightening insights into fundamental physics in moiré superlattice systems and guides for designing novel devices. In this review, first, a brief introduction is given on advanced ARPES techniques and basic ideas of band structures in a moiré superlattice system. Then ARPES research results of various moiré superlattice systems are highlighted, including graphene on substrates with small lattice mismatches, twisted graphene/TMD moiré systems, and high-order moiré superlattice systems. Finally, it discusses important questions that remain open, challenges in current experimental investigations, and presents an outlook on this field of research.
Collapse
Affiliation(s)
- Yiwei Li
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
| | - Qiang Wan
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
| | - Nan Xu
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
- Wuhan Institute of Quantum Technology, Wuhan, 430206, China
| |
Collapse
|
32
|
Uri A, de la Barrera SC, Randeria MT, Rodan-Legrain D, Devakul T, Crowley PJD, Paul N, Watanabe K, Taniguchi T, Lifshitz R, Fu L, Ashoori RC, Jarillo-Herrero P. Superconductivity and strong interactions in a tunable moiré quasicrystal. Nature 2023; 620:762-767. [PMID: 37468640 DOI: 10.1038/s41586-023-06294-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Accepted: 06/07/2023] [Indexed: 07/21/2023]
Abstract
Electronic states in quasicrystals generally preclude a Bloch description1, rendering them fascinating and enigmatic. Owing to their complexity and scarcity, quasicrystals are underexplored relative to periodic and amorphous structures. Here we introduce a new type of highly tunable quasicrystal easily assembled from periodic components. By twisting three layers of graphene with two different twist angles, we form two mutually incommensurate moiré patterns. In contrast to many common atomic-scale quasicrystals2,3, the quasiperiodicity in our system is defined on moiré length scales of several nanometres. This 'moiré quasicrystal' allows us to tune the chemical potential and thus the electronic system between a periodic-like regime at low energies and a strongly quasiperiodic regime at higher energies, the latter hosting a large density of weakly dispersing states. Notably, in the quasiperiodic regime, we observe superconductivity near a flavour-symmetry-breaking phase transition4,5, the latter indicative of the important role that electronic interactions play in that regime. The prevalence of interacting phenomena in future systems with in situ tunability is not only useful for the study of quasiperiodic systems but may also provide insights into electronic ordering in related periodic moiré crystals6-12. We anticipate that extending this platform to engineer quasicrystals by varying the number of layers and twist angles, and by using different two-dimensional components, will lead to a new family of quantum materials to investigate the properties of strongly interacting quasicrystals.
Collapse
Affiliation(s)
- Aviram Uri
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | | | - Mallika T Randeria
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Daniel Rodan-Legrain
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Trithep Devakul
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Philip J D Crowley
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Nisarga Paul
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Ron Lifshitz
- Raymond & Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Tel Aviv, Israel
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Raymond C Ashoori
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | |
Collapse
|
33
|
Nuckolls KP, Lee RL, Oh M, Wong D, Soejima T, Hong JP, Călugăru D, Herzog-Arbeitman J, Bernevig BA, Watanabe K, Taniguchi T, Regnault N, Zaletel MP, Yazdani A. Quantum textures of the many-body wavefunctions in magic-angle graphene. Nature 2023; 620:525-532. [PMID: 37587297 DOI: 10.1038/s41586-023-06226-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 05/16/2023] [Indexed: 08/18/2023]
Abstract
Interactions among electrons create novel many-body quantum phases of matter with wavefunctions that reflect electronic correlation effects, broken symmetries and collective excitations. Many quantum phases have been discovered in magic-angle twisted bilayer graphene (MATBG), including correlated insulating1, unconventional superconducting2-5 and magnetic topological6-9 phases. The lack of microscopic information10,11 of possible broken symmetries has hampered our understanding of these phases12-17. Here we use high-resolution scanning tunnelling microscopy to study the wavefunctions of the correlated phases in MATBG. The squares of the wavefunctions of gapped phases, including those of the correlated insulating, pseudogap and superconducting phases, show distinct broken-symmetry patterns with a √3 × √3 super-periodicity on the graphene atomic lattice that has a complex spatial dependence on the moiré scale. We introduce a symmetry-based analysis using a set of complex-valued local order parameters, which show intricate textures that distinguish the various correlated phases. We compare the observed quantum textures of the correlated insulators at fillings of ±2 electrons per moiré unit cell to those expected for proposed theoretical ground states. In typical MATBG devices, these textures closely match those of the proposed incommensurate Kekulé spiral order15, whereas in ultralow-strain samples, our data have local symmetries like those of a time-reversal symmetric intervalley coherent phase12. Moreover, the superconducting state of MATBG shows strong signatures of intervalley coherence, only distinguishable from those of the insulator with our phase-sensitive measurements.
Collapse
Affiliation(s)
- Kevin P Nuckolls
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Ryan L Lee
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Myungchul Oh
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Dillon Wong
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Tomohiro Soejima
- Department of Physics, University of California, Berkeley, CA, USA
| | - Jung Pyo Hong
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Dumitru Călugăru
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Jonah Herzog-Arbeitman
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - B Andrei Bernevig
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
- Donostia International Physics Center, Donostia-San Sebastian, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Nicolas Regnault
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - Michael P Zaletel
- Department of Physics, University of California, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Ali Yazdani
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA.
| |
Collapse
|
34
|
Sainz-Cruz H, Pantaleón PA, Phong VT, Jimeno-Pozo A, Guinea F. Junctions and Superconducting Symmetry in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2023; 131:016003. [PMID: 37478460 DOI: 10.1103/physrevlett.131.016003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 05/31/2023] [Indexed: 07/23/2023]
Abstract
Junctions provide a wealth of information on the symmetry of the order parameter of superconductors. We analyze junctions between a scanning tunneling microscope (STM) tip and superconducting twisted bilayer graphene (TBG) and TBG Josephson junctions (JJs). We compare superconducting phases that are even or odd under valley exchange (s- or f-wave). The critical current in mixed (s and f) JJs strongly depends on the angle between the junction and the lattice. In STM-TBG junctions, due to Andreev reflection, the f-wave leads to a prominent peak in subgap conductance, as seen in experiments.
Collapse
Affiliation(s)
| | | | - Võ Tiến Phong
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | | | - Francisco Guinea
- Imdea Nanoscience, Faraday 9, 28015 Madrid, Spain
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastian, Spain
| |
Collapse
|
35
|
Sitek J, Czerniak-Łosiewicz K, Gertych AP, Giza M, Dąbrowski P, Rogala M, Wilczyński K, Kaleta A, Kret S, Conran BR, Wang X, McAleese C, Macha M, Radenović A, Zdrojek M, Pasternak I, Strupiński W. Selective Growth of van der Waals Heterostructures Enabled by Electron-Beam Irradiation. ACS APPLIED MATERIALS & INTERFACES 2023. [PMID: 37418753 PMCID: PMC10360032 DOI: 10.1021/acsami.3c02892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/09/2023]
Abstract
Van der Waals heterostructures (vdWHSs) enable the fabrication of complex electronic devices based on two-dimensional (2D) materials. Ideally, these vdWHSs should be fabricated in a scalable and repeatable way and only in the specific areas of the substrate to lower the number of technological operations inducing defects and impurities. Here, we present a method of selective fabrication of vdWHSs via chemical vapor deposition by electron-beam (EB) irradiation. We distinguish two growth modes: positive (2D materials nucleate on the irradiated regions) on graphene and tungsten disulfide (WS2) substrates, and negative (2D materials do not nucleate on the irradiated regions) on the graphene substrate. The growth mode is controlled by limiting the air exposure of the irradiated substrate and the time between irradiation and growth. We conducted Raman mapping, Kelvin-probe force microscopy, X-ray photoelectron spectroscopy, and density-functional theory modeling studies to investigate the selective growth mechanism. We conclude that the selective growth is explained by the competition of three effects: EB-induced defects, adsorption of carbon species, and electrostatic interaction. The method here is a critical step toward the industry-scale fabrication of 2D-materials-based devices.
Collapse
Affiliation(s)
- Jakub Sitek
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
- CENTERA Laboratory, Institute for High Pressure Physics, Polish Academy of Sciences, Sokołowska 29, 01-142 Warsaw, Poland
| | | | - Arkadiusz P Gertych
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
| | - Małgorzata Giza
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
| | - Paweł Dąbrowski
- Faculty of Physics and Applied Informatics, University of Łódź, Pomorska 149/153, 90-236 Łódź, Poland
| | - Maciej Rogala
- Faculty of Physics and Applied Informatics, University of Łódź, Pomorska 149/153, 90-236 Łódź, Poland
| | - Konrad Wilczyński
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
| | - Anna Kaleta
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
| | - Sławomir Kret
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
| | - Ben R Conran
- AIXTRON Ltd, Buckingway Business Park, Anderson Road, Swavesey, Cambridge CB24 4FQ, U.K
| | - Xiaochen Wang
- AIXTRON Ltd, Buckingway Business Park, Anderson Road, Swavesey, Cambridge CB24 4FQ, U.K
| | - Clifford McAleese
- AIXTRON Ltd, Buckingway Business Park, Anderson Road, Swavesey, Cambridge CB24 4FQ, U.K
| | - Michał Macha
- Laboratory of Nanoscale Biology, Swiss Federal Institute of Technology Lausanne (EPFL), Station 17, CH-015 Lausanne, Switzerland
| | - Aleksandra Radenović
- Laboratory of Nanoscale Biology, Swiss Federal Institute of Technology Lausanne (EPFL), Station 17, CH-015 Lausanne, Switzerland
| | - Mariusz Zdrojek
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
| | - Iwona Pasternak
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
| | - Włodek Strupiński
- Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
| |
Collapse
|
36
|
Hu JX, Sun ZT, Xie YM, Law KT. Josephson Diode Effect Induced by Valley Polarization in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2023; 130:266003. [PMID: 37450809 DOI: 10.1103/physrevlett.130.266003] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Accepted: 05/26/2023] [Indexed: 07/18/2023]
Abstract
Recently, the Josephson diode effect (JDE), in which the superconducting critical current magnitudes differ when the currents flow in opposite directions, has attracted great interest. In particular, it was demonstrated that gate-defined Josephson junctions based on magic-angle twisted bilayer graphene showed a strong nonreciprocal effect when the weak-link region is gated to a correlated insulating state at half filling (two holes per moiré cell). However, the mechanism behind such a phenomenon is not yet understood. In this Letter, we show that the interaction-driven valley polarization, together with the trigonal warping of the Fermi surface, induce the JDE. The valley polarization, which lifts the degeneracy of the states in the two valleys, induces a relative phase difference between the first and the second harmonics of the supercurrent and results in the JDE. We further show that the nontrivial current phase relation, which is responsible for the JDE, also generates the asymmetric Shapiro steps.
Collapse
Affiliation(s)
- Jin-Xin Hu
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Zi-Ting Sun
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Ying-Ming Xie
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - K T Law
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| |
Collapse
|
37
|
Dong Q, Pan J, Li S, Li C, Lin T, Liu B, Liu R, Li Q, Huang F, Liu B. Abnormal Metal-Semiconductor-Like Transition and Exceptional Enhanced Superconducting State in Pressurized Restacked TaS 2. J Am Chem Soc 2023. [PMID: 37364244 DOI: 10.1021/jacs.3c03560] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
Interlayer coupling and stacking order play essential roles in shaping the exotic electronic properties of two-dimensional materials. Here, we employ restacked TaS2─a novel transition metal dichalcogenide (TMD) with weak vdW bonding and twisted angles─to investigate the strain effects of interlayer modulation on the electronic properties. Under pressure, an unexpected transition from metallic to semiconducting-like states occurs. Superconductivity coexists with the semiconducting-like state over a wide pressure range, which has never before been observed in TMDs. Upon further compression, a new superconducting SC-II state emerges without structural evolution and gradually replaces the initial SC-I state. The emerging SC-II state exhibits robust zero-resistance superconductivity and an ultrahigh upper critical field. The abundant electronic state changes in RS-TaS2 are strongly related to band-structure engineering resulting from pressure-induced interlayer stacking angle modulation. Our results reveal the remarkable effect of interlayer rearrangement on electronic properties and provide a special way to explore the unique properties of 2D materials.
Collapse
Affiliation(s)
- Qing Dong
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Jie Pan
- School of Flexible Electronics (Future Technologies), Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China
- State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
| | - Shujia Li
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Chenyi Li
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Tao Lin
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Bo Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Ran Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Quanjun Li
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| | - Fuqiang Huang
- State Key Laboratory of High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
- State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Bingbing Liu
- State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
| |
Collapse
|
38
|
Sukhachov PO, von Oppen F, Glazman LI. Andreev Reflection in Scanning Tunneling Spectroscopy of Unconventional Superconductors. PHYSICAL REVIEW LETTERS 2023; 130:216002. [PMID: 37295098 DOI: 10.1103/physrevlett.130.216002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 05/02/2023] [Indexed: 06/12/2023]
Abstract
We evaluate the differential conductance measured in an STM setting at arbitrary electron transmission between STM tip and a 2D superconductor with arbitrary gap structure. Our analytical scattering theory accounts for Andreev reflections, which become prominent at larger transmissions. We show that this provides complementary information about the superconducting gap structure beyond the tunneling density of states, strongly facilitating the ability to extract the gap symmetry and its relation to the underlying crystalline lattice. We use the developed theory to discuss recent experimental results on superconductivity in twisted bilayer graphene.
Collapse
Affiliation(s)
- P O Sukhachov
- Department of Physics, Yale University, New Haven, Connecticut 06520, USA
| | - Felix von Oppen
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - L I Glazman
- Department of Physics, Yale University, New Haven, Connecticut 06520, USA
| |
Collapse
|
39
|
Curtis JB, Poniatowski NR, Xie Y, Yacoby A, Demler E, Narang P. Stabilizing Fluctuating Spin-Triplet Superconductivity in Graphene via Induced Spin-Orbit Coupling. PHYSICAL REVIEW LETTERS 2023; 130:196001. [PMID: 37243633 DOI: 10.1103/physrevlett.130.196001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 04/11/2023] [Indexed: 05/29/2023]
Abstract
A recent experiment showed that a proximity-induced Ising spin-orbit coupling enhances the spin-triplet superconductivity in Bernal bilayer graphene. Here, we show that, due to the nearly perfect spin rotation symmetry of graphene, the fluctuations of the spin orientation of the triplet order parameter suppress the superconducting transition to nearly zero temperature. Our analysis shows that both an Ising spin-orbit coupling and an in-plane magnetic field can eliminate these low-lying fluctuations and can greatly enhance the transition temperature, consistent with the recent experiment. Our model also suggests the possible existence of a phase at small anisotropy and magnetic field which exhibits quasilong-range ordered spin-singlet charge 4e superconductivity, even while the triplet 2e superconducting order only exhibits short-ranged correlations. Finally, we discuss relevant experimental signatures.
Collapse
Affiliation(s)
- Jonathan B Curtis
- College of Letters and Science, University of California, Los Angeles, California 90095, USA
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | | | - Yonglong Xie
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Amir Yacoby
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Eugene Demler
- Institute for Theoretical Physics, ETH Zürich, 8093 Zürich, Switzerland
| | - Prineha Narang
- College of Letters and Science, University of California, Los Angeles, California 90095, USA
| |
Collapse
|
40
|
Kim HL, Wang F. Reflective Phase-Contrast for High-Contrast Imaging of van der Waals Heterostructure. NANO LETTERS 2023; 23:2898-2904. [PMID: 36921228 DOI: 10.1021/acs.nanolett.3c00252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Optical microscopy plays a critical role in the fabrication of two-dimensional (2D) van der Waals heterostructures. An outstanding challenge in conventional microscopy is to visualize transparent 2D layers as well as embedded monolayers in a stacked heterostructure with high optical contrast. Phase-contrast microscopy, first developed by Frits Zernike in the 1930s, leverages the interference effect between specimen scattered light and background light to increase the contrast of transparent specimens. Such phase-contrast microscopy, always in a transmission configuration, revolutionized the study of transparent cellular structures in biology. Here, we develop a versatile reflective phase-contrast microscopy for imaging 2D heterostructures. We employ two spatial light modulators to flexibly control the intensity and phase of the illumination and the reflected light. This reflective phase-contrast microscopy achieves unprecedented high contrast for imaging a transparent 2D monolayer. It also enables direct observation of 2D monolayers embedded inside a thick heterostructure that are "invisible" in conventional microscopy.
Collapse
Affiliation(s)
- Ha-Leem Kim
- Department of Physics, University of California, Berkeley, California 94720, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Feng Wang
- Department of Physics, University of California, Berkeley, California 94720, United States
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| |
Collapse
|
41
|
Jarjour A, Ferguson GM, Schaefer BT, Lee M, Loh YL, Trivedi N, Nowack KC. Superfluid response of an atomically thin gate-tuned van der Waals superconductor. Nat Commun 2023; 14:2055. [PMID: 37045826 PMCID: PMC10097715 DOI: 10.1038/s41467-023-37210-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Accepted: 03/03/2023] [Indexed: 04/14/2023] Open
Abstract
A growing number of two-dimensional superconductors are being discovered in the family of exfoliated van der Waals materials. Due to small sample volume, the superfluid response of these materials has not been characterized. Here, we use a local magnetic probe to directly measure this key property of the tunable, gate-induced superconducting state in MoS2. We find that the backgate changes the transition temperature non-monotonically whereas the superfluid stiffness at low temperature and the normal state conductivity monotonically increase. In some devices, we find direct signatures in agreement with a Berezinskii-Kosterlitz-Thouless transition, whereas in others we find a broadened onset of the superfluid response. We show that the observed behavior is consistent with disorder playing an important role in determining the properties of superconducting MoS2. Our work demonstrates that magnetic property measurements are within reach for superconducting devices based on exfoliated sheets and reveals that the superfluid response significantly deviates from simple BCS-like behavior.
Collapse
Affiliation(s)
- Alexander Jarjour
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
| | - G M Ferguson
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
| | - Brian T Schaefer
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA
| | - Menyoung Lee
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA
- School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA
| | - Yen Lee Loh
- Department of Physics and Astrophysics, University of North Dakota, Grand Forks, ND, USA
| | - Nandini Trivedi
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Katja C Nowack
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
| |
Collapse
|
42
|
Aggarwal D, Narula R, Ghosh S. A primer on twistronics: a massless Dirac fermion's journey to moiré patterns and flat bands in twisted bilayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:143001. [PMID: 36745922 DOI: 10.1088/1361-648x/acb984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 02/06/2023] [Indexed: 06/18/2023]
Abstract
The recent discovery of superconductivity in magic-angle twisted bilayer graphene (TBLG) has sparked a renewed interest in the strongly-correlated physics ofsp2carbons, in stark contrast to preliminary investigations which were dominated by the one-body physics of the massless Dirac fermions. We thus provide a self-contained, theoretical perspective of the journey of graphene from its single-particle physics-dominated regime to the strongly-correlated physics of the flat bands. Beginning from the origin of the Dirac points in condensed matter systems, we discuss the effect of the superlattice on the Fermi velocity and Van Hove singularities in graphene and how it leads naturally to investigations of the moiré pattern in van der Waals heterostructures exemplified by graphene-hexagonal boron-nitride and TBLG. Subsequently, we illuminate the origin of flat bands in TBLG at the magic angles by elaborating on a broad range of prominent theoretical works in a pedagogical way while linking them to available experimental support, where appropriate. We conclude by providing a list of topics in the study of the electronic properties of TBLG not covered by this review but may readily be approached with the help of this primer.
Collapse
Affiliation(s)
| | - Rohit Narula
- Department of Physics, IIT Delhi, Hauz Khas, New Delhi, India
| | - Sankalpa Ghosh
- Department of Physics, IIT Delhi, Hauz Khas, New Delhi, India
| |
Collapse
|
43
|
Tian H, Gao X, Zhang Y, Che S, Xu T, Cheung P, Watanabe K, Taniguchi T, Randeria M, Zhang F, Lau CN, Bockrath MW. Evidence for Dirac flat band superconductivity enabled by quantum geometry. Nature 2023; 614:440-444. [PMID: 36792742 DOI: 10.1038/s41586-022-05576-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 11/18/2022] [Indexed: 02/17/2023]
Abstract
In a flat band superconductor, the charge carriers' group velocity vF is extremely slow. Superconductivity therein is particularly intriguing, being related to the long-standing mysteries of high-temperature superconductors1 and heavy-fermion systems2. Yet the emergence of superconductivity in flat bands would appear paradoxical, as a small vF in the conventional Bardeen-Cooper-Schrieffer theory implies vanishing coherence length, superfluid stiffness and critical current. Here, using twisted bilayer graphene3-7, we explore the profound effect of vanishingly small velocity in a superconducting Dirac flat band system8-13. Using Schwinger-limited non-linear transport studies14,15, we demonstrate an extremely slow normal state drift velocity vn ≈ 1,000 m s-1 for filling fraction ν between -1/2 and -3/4 of the moiré superlattice. In the superconducting state, the same velocity limit constitutes a new limiting mechanism for the critical current, analogous to a relativistic superfluid16. Importantly, our measurement of superfluid stiffness, which controls the superconductor's electrodynamic response, shows that it is not dominated by the kinetic energy but instead by the interaction-driven superconducting gap, consistent with recent theories on a quantum geometric contribution8-12. We find evidence for small Cooper pairs, characteristic of the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover17-19, with an unprecedented ratio of the superconducting transition temperature to the Fermi temperature exceeding unity and discuss how this arises for ultra-strong coupling superconductivity in ultra-flat Dirac bands.
Collapse
Affiliation(s)
- Haidong Tian
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Xueshi Gao
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Yuxin Zhang
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Shi Che
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Tianyi Xu
- Department of Physics, The University of Texas at Dallas, Richardson, TX, USA
| | - Patrick Cheung
- Department of Physics, The University of Texas at Dallas, Richardson, TX, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Mohit Randeria
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Fan Zhang
- Department of Physics, The University of Texas at Dallas, Richardson, TX, USA
| | - Chun Ning Lau
- Department of Physics, The Ohio State University, Columbus, OH, USA.
| | - Marc W Bockrath
- Department of Physics, The Ohio State University, Columbus, OH, USA.
| |
Collapse
|
44
|
Acharjee S, Dutta N, Devi R, Boruah A. Nonlinear oscillations, chaotic dynamics, and stability analysis of bilayer graphene-like structures. CHAOS (WOODBURY, N.Y.) 2023; 33:013136. [PMID: 36725664 DOI: 10.1063/5.0125665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 12/26/2022] [Indexed: 06/18/2023]
Abstract
In this work, we have investigated the nonlinear oscillations and chaotic dynamics of perturbed bilayer graphene-like structures. The potential energy surface (PES) of bilayer graphene-like geometries is obtained by considering interactions of a co-aligned and counter-aligned arrangement of atoms. We studied the dynamics using the Poincaré surface of section for co-aligned hydrofluorinated graphene (HFG) and counter-aligned hexagonal boron nitride (h-BN) and generalized it for other systems using various choices of interaction parameters. The nature of the oscillations is understood via power spectra and the Lyapunov exponents. We found that the PES is very sensitive to the perturbation for all bilayer graphene-like systems. It is seen that the bilayer HFG system displays chaotic oscillations for strong perturbation, while for the h-BN system, the signature of chaos is found for weak perturbation. We have also generalized the work for perturbed bilayer graphene-like geometries, considering different interlayer interactions and the strength of perturbation. We found a signature of transition from regular to quasiperiodic and finally chaotic oscillations tuned via the strength of the perturbation for these geometries. The nature of the equilibrium points for bilayer graphene-like systems is analyzed via Jacobian stability conditions. We found three stable nodes for co-aligned HFG and counter-aligned h-BN systems for all interaction strengths. Though all other nodes are unstable saddle nodes, the signature of a local bifurcation is also found for weak perturbation.
Collapse
Affiliation(s)
- Saumen Acharjee
- Department of Physics, Dibrugarh University, Dibrugarh 786 004, Assam, India
| | - Nimisha Dutta
- Department of Physics, Dibrugarh University, Dibrugarh 786 004, Assam, India
| | - Reeta Devi
- Department of Physics, Dibrugarh University, Dibrugarh 786 004, Assam, India
| | - Arindam Boruah
- Department of Physics, Dibrugarh University, Dibrugarh 786 004, Assam, India
| |
Collapse
|
45
|
Talantsev EF. The Compliance of the Upper Critical Field in Magic-Angle Multilayer Graphene with the Pauli Limit. MATERIALS (BASEL, SWITZERLAND) 2022; 16:256. [PMID: 36614595 PMCID: PMC9822272 DOI: 10.3390/ma16010256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Revised: 12/10/2022] [Accepted: 12/23/2022] [Indexed: 06/17/2023]
Abstract
The Pauli limiting field represents a fundamental magnetic field at which the superconducting state collapses due to the spin-paramagnetic Cooper pair-breaking effect. Cao et al. (Nature 2021, 595, 526) reported that the magic-angle twisted trilayer graphene (MATNG, N = 3) exhibits the upper critical field which exceeds the Pauli limiting field by two to three times. This observation was interpreted as a violation of the Pauli-limiting field in MAT3G. Similar conclusions were recently reported by the same research group in MATNG (N = 4, 5) superlattices (Park, J.M. et al. Nat. Mater.2022, 21, 877). Here, we point out that Cao et al. (Nature 2021, 595, 526) calculated the Pauli limiting field by the use of reduced form (to the weak-coupling limit) of full equation of the theory of the electron−phonon-mediated superconductivity. Considering that in the same paper, Cao et al. (Nature 2021, 595, 526) reported that MATNGs are strong coupled superconductors, we calculate the Pauli limiting field for a strong coupled case and show that the observed upper critical fields in MATNGs comply with the Pauli limit. This implies that there is no violation of the Pauli limiting field in the Moiré multilayer graphene superlattices.
Collapse
Affiliation(s)
- Evgueni F Talantsev
- M. N. Miheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, 18, S. Kovalevskoy St., 620108 Ekaterinburg, Russia
| |
Collapse
|
46
|
Portolés E, Iwakiri S, Zheng G, Rickhaus P, Taniguchi T, Watanabe K, Ihn T, Ensslin K, de Vries FK. A tunable monolithic SQUID in twisted bilayer graphene. NATURE NANOTECHNOLOGY 2022; 17:1159-1164. [PMID: 36280761 DOI: 10.1038/s41565-022-01222-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 09/05/2022] [Indexed: 06/16/2023]
Abstract
Magic-angle twisted bilayer graphene (MATBG) hosts a number of correlated states of matter that can be tuned by electrostatic doping1-4. Transport5,6 and scanning-probe7-9 experiments have shown evidence for band, correlated and Chern insulators along with superconductivity. This variety of in situ tunable states has allowed for the realization of tunable Josephson junctions10-12. However, although phase-coherent phenomena have been measured10-12, no control of the phase difference of the superconducting condensates has been demonstrated so far. Here we build on previous gate-defined junction realizations and form a superconducting quantum interference device13 (SQUID) in MATBG, where the superconducting phase difference is controlled through the magnetic field. We observe magneto-oscillations of the critical current, demonstrating long-range coherence of superconducting charge carriers with an effective charge of 2e. We tune to both asymmetric and symmetric SQUID configurations by electrostatically controlling the critical currents through the junctions. This tunability allows us to study the inductances in the device, finding values of up to 2 μH. Furthermore, we directly probe the current-phase relation of one of the junctions of the device. Our results show that complex devices in MATBG can be realized and used to reveal the properties of the material. We envision our findings, together with the established history of applications SQUIDs have14-16, will foster the development of a wide range of devices such as phase-slip junctions17 or high kinetic inductance detectors18.
Collapse
Affiliation(s)
- Elías Portolés
- Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland.
| | - Shuichi Iwakiri
- Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland
| | - Giulia Zheng
- Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland
| | - Peter Rickhaus
- Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland
- Quantum Center, ETH Zurich, Zurich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zurich, Zurich, Switzerland.
- Quantum Center, ETH Zurich, Zurich, Switzerland.
| | | |
Collapse
|
47
|
Spontaneous time-reversal symmetry breaking in twisted double bilayer graphene. Nat Commun 2022; 13:6468. [PMID: 36309518 PMCID: PMC9617879 DOI: 10.1038/s41467-022-34192-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Accepted: 10/12/2022] [Indexed: 11/08/2022] Open
Abstract
Twisted double bilayer graphene (tDBG) comprises two Bernal-stacked bilayer graphene sheets with a twist between them. Gate voltages applied to top and back gates of a tDBG device tune both the flatness and topology of the electronic bands, enabling an unusual level of experimental control. Metallic states with broken spin and valley symmetries have been observed in tDBG devices with twist angles in the range 1.2–1.3°, but the topologies and order parameters of these states have remained unclear. We report the observation of an anomalous Hall effect in the correlated metal state of tDBG, with hysteresis loops spanning hundreds of mT in out-of-plane magnetic field (B⊥) that demonstrate spontaneously broken time-reversal symmetry. The B⊥ hysteresis persists for in-plane fields up to several Tesla, suggesting valley (orbital) ferromagnetism. At the same time, the resistivity is strongly affected by even mT-scale values of in-plane magnetic field, pointing to spin-valley coupling or to a direct orbital coupling between in-plane field and the valley degree of freedom. Twisted double bilayer graphene (tDBG) comprises two Bernal-stacked bilayer graphene sheets with a twist between them. Here, the authors report a strong anomalous Hall effect in the correlated-metal regime of tDBG, indicating time reversal symmetry breaking from orbital ferromagnetism, likely associated with valley polarization.
Collapse
|
48
|
Zhang Y, Polski R, Lewandowski C, Thomson A, Peng Y, Choi Y, Kim H, Watanabe K, Taniguchi T, Alicea J, von Oppen F, Refael G, Nadj-Perge S. Promotion of superconductivity in magic-angle graphene multilayers. Science 2022; 377:1538-1543. [PMID: 36173835 DOI: 10.1126/science.abn8585] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Graphene moiré superlattices show an abundance of correlated insulating, topological, and superconducting phases. Whereas the origins of strong correlations and nontrivial topology can be directly linked to flat bands, the nature of superconductivity remains enigmatic. We demonstrate that magic-angle devices made of twisted tri-, quadri-, and pentalayer graphene placed on monolayer tungsten diselenide exhibit flavor polarization and superconductivity. We also observe insulating states in the tril- and quadrilayer arising at finite electric displacement fields. As the number of layers increases, superconductivity emerges over an enhanced filling-factor range, and in the pentalayer it extends well beyond the filling of four electrons per moiré unit cell. Our results highlight the role of the interplay between flat and more dispersive bands in extending superconducting regions in graphene moiré superlattices.
Collapse
Affiliation(s)
- Yiran Zhang
- T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Robert Polski
- T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Cyprian Lewandowski
- Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Alex Thomson
- Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, University of California, Davis, CA 95616, USA
| | - Yang Peng
- Department of Physics and Astronomy, California State University, Northridge, CA 91330, USA
| | - Youngjoon Choi
- T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Hyunjin Kim
- T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305 0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305 0044, Japan
| | - Jason Alicea
- Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Felix von Oppen
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Gil Refael
- Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| | - Stevan Nadj-Perge
- T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA.,Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
| |
Collapse
|
49
|
Wang X, Liu N, Wu Y, Qu Y, Zhang W, Wang J, Guan D, Wang S, Zheng H, Li Y, Liu C, Jia J. Strong Coupling Superconductivity in Ca-Intercalated Bilayer Graphene on SiC. NANO LETTERS 2022; 22:7651-7658. [PMID: 36066512 DOI: 10.1021/acs.nanolett.2c02804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The metal-intercalated bilayer graphene has a flat band with a high density of states near the Fermi energy and thus is anticipated to exhibit an enhanced strong correlation effect and associated fascinating phenomena, including superconductivity. By using a self-developed multifunctional scanning tunneling microscope, we succeeded in observing the superconducting energy gap and diamagnetic response of a Ca-intercalated bilayer graphene below a critical temperature of 8.83 K. The revealed high value of gap ratio, 2Δ/kBTc ≈ 5.0, indicates a strong coupling superconductivity, while the variation of penetration depth with temperature and magnetic field indicates an isotropic s-wave superconductor. These results provide crucial experimental clues for understanding the origin and mechanism of superconductivity in carrier-doped graphene.
Collapse
Affiliation(s)
- Xutao Wang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
| | - Ningning Liu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
| | - Yanfu Wu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
| | - Yueqiao Qu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
| | - Wenxuan Zhang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
| | - Jinyue Wang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
| | - Dandan Guan
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
| | - Shiyong Wang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
| | - Hao Zheng
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
| | - Yaoyi Li
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
| | - Canhua Liu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
- Tsung-Dao Lee Institute, Shanghai 200240, People's Republic of China
| | - Jinfeng Jia
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China
- Tsung-Dao Lee Institute, Shanghai 200240, People's Republic of China
| |
Collapse
|
50
|
Das P, Chattopadhyay A. Enhanced Chemical Stability in the Twisted Dodecagonal Stacking of Two-Dimensional Copper Nanocluster Assemblies. J Phys Chem Lett 2022; 13:8793-8800. [PMID: 36103686 DOI: 10.1021/acs.jpclett.2c02300] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Deterministic chemical stacking of two-dimensional materials with controlled symmetry is a synthetic chemistry challenge that deserves attention. It is plausible that depending on the angle of stacking the material properties of the assembly could be tuned. Herein, we report 30° twisted stacking of two-dimensional nanosheets of a hexagonal assembly of organic ligand-stabilized Cu nanoclusters formed through a Zn2+-mediated complexation reaction. Electron diffraction in transmission electron microscopy revealed the presence of regions of dodecagonal symmetry with the apparent loss of translation symmetry. Photoluminescence measurements indicated the formation of the stacked assembly in the liquid medium. The as-synthesized twisted stacking structure exhibited superior delayed photoluminescence and chemical stability─in the presence of molecular iodine─as compared to the hexagonal crystal. The discovery can lead to a bright future in exploring new chemical and physical properties through the design of stacked assemblies of luminescent or other materials.
Collapse
|