201
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Kazmierczak NP, Van Winkle M, Ophus C, Bustillo KC, Carr S, Brown HG, Ciston J, Taniguchi T, Watanabe K, Bediako DK. Strain fields in twisted bilayer graphene. NATURE MATERIALS 2021; 20:956-963. [PMID: 33859383 DOI: 10.1038/s41563-021-00973-w] [Citation(s) in RCA: 60] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 03/02/2021] [Indexed: 05/27/2023]
Abstract
Van der Waals heteroepitaxy allows deterministic control over lattice mismatch or azimuthal orientation between atomic layers to produce long-wavelength superlattices. The resulting electronic phases depend critically on the superlattice periodicity and localized structural deformations that introduce disorder and strain. In this study we used Bragg interferometry to capture atomic displacement fields in twisted bilayer graphene with twist angles <2°. Nanoscale spatial fluctuations in twist angle and uniaxial heterostrain were statistically evaluated, revealing the prevalence of short-range disorder in moiré heterostructures. By quantitatively mapping strain tensor fields, we uncovered two regimes of structural relaxation and disentangled the electronic contributions of constituent rotation modes. Further, we found that applied heterostrain accumulates anisotropically in saddle-point regions, generating distinctive striped strain phases. Our results establish the reconstruction mechanics underpinning the twist-angle-dependent electronic behaviour of twisted bilayer graphene and provide a framework for directly visualizing structural relaxation, disorder and strain in moiré materials.
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Affiliation(s)
- Nathanael P Kazmierczak
- Department of Chemistry, University of California, Berkeley, CA, USA
- Department of Chemistry and Biochemistry, Calvin University, Grand Rapids, MI, USA
| | | | - Colin Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Karen C Bustillo
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Stephen Carr
- Department of Physics, Brown University, Providence, RI, USA
- Brown Theoretical Physics Center, Brown University, Providence, RI, USA
| | - Hamish G Brown
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Jim Ciston
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 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
| | - D Kwabena Bediako
- Department of Chemistry, University of California, Berkeley, CA, USA.
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
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202
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Jin C, Tao Z, Li T, Xu Y, Tang Y, Zhu J, Liu S, Watanabe K, Taniguchi T, Hone JC, Fu L, Shan J, Mak KF. Stripe phases in WSe 2/WS 2 moiré superlattices. NATURE MATERIALS 2021; 20:940-944. [PMID: 33767398 DOI: 10.1038/s41563-021-00959-8] [Citation(s) in RCA: 58] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Accepted: 02/12/2021] [Indexed: 06/12/2023]
Abstract
Stripe phases, in which the rotational symmetry of charge density is spontaneously broken, occur in many strongly correlated systems with competing interactions1-11. However, identifying and studying such stripe phases remains challenging. Here we uncover stripe phases in WSe2/WS2 moiré superlattices by combining optical anisotropy and electronic compressibility measurements. We find strong electronic anisotropy over a large doping range peaked at 1/2 filling of the moiré superlattice. The 1/2 state is incompressible and assigned to an insulating stripe crystal phase. Wide-field imaging reveals domain configurations with a preferential alignment along the high-symmetry axes of the moiré superlattice. Away from 1/2 filling, we observe additional stripe crystals at commensurate filling 1/4, 2/5 and 3/5, and compressible electronic liquid crystal states at incommensurate fillings. Our results demonstrate that two-dimensional semiconductor moiré superlattices are a highly tunable platform from which to study the stripe phases and their interplay with other symmetry breaking ground states.
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Affiliation(s)
- Chenhao Jin
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
| | - Zui Tao
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Tingxin Li
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Yang Xu
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Yanhao Tang
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Jiacheng Zhu
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Song Liu
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - James C Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Jie Shan
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
| | - Kin Fai Mak
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
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203
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Signatures of Wigner crystal of electrons in a monolayer semiconductor. Nature 2021; 595:53-57. [PMID: 34194018 DOI: 10.1038/s41586-021-03590-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 04/28/2021] [Indexed: 11/09/2022]
Abstract
When the Coulomb repulsion between electrons dominates over their kinetic energy, electrons in two-dimensional systems are predicted to spontaneously break continuous-translation symmetry and form a quantum crystal1. Efforts to observe2-12 this elusive state of matter, termed a Wigner crystal, in two-dimensional extended systems have primarily focused on conductivity measurements on electrons confined to a single Landau level at high magnetic fields. Here we use optical spectroscopy to demonstrate that electrons in a monolayer semiconductor with density lower than 3 × 1011 per centimetre squared form a Wigner crystal. The combination of a high electron effective mass and reduced dielectric screening enables us to observe electronic charge order even in the absence of a moiré potential or an external magnetic field. The interactions between a resonantly injected exciton and electrons arranged in a periodic lattice modify the exciton bandstructure so that an umklapp resonance arises in the optical reflection spectrum, heralding the presence of charge order13. Our findings demonstrate that charge-tunable transition metal dichalcogenide monolayers14 enable the investigation of previously uncharted territory for many-body physics where interaction energy dominates over kinetic energy.
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204
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Miao S, Wang T, Huang X, Chen D, Lian Z, Wang C, Blei M, Taniguchi T, Watanabe K, Tongay S, Wang Z, Xiao D, Cui YT, Shi SF. Strong interaction between interlayer excitons and correlated electrons in WSe 2/WS 2 moiré superlattice. Nat Commun 2021; 12:3608. [PMID: 34127668 PMCID: PMC8203657 DOI: 10.1038/s41467-021-23732-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 05/10/2021] [Indexed: 11/22/2022] Open
Abstract
Heterobilayers of transition metal dichalcogenides (TMDCs) can form a moiré superlattice with flat minibands, which enables strong electron interaction and leads to various fascinating correlated states. These heterobilayers also host interlayer excitons in a type-II band alignment, in which optically excited electrons and holes reside on different layers but remain bound by the Coulomb interaction. Here we explore the unique setting of interlayer excitons interacting with strongly correlated electrons, and we show that the photoluminescence (PL) of interlayer excitons sensitively signals the onset of various correlated insulating states as the band filling is varied. When the system is in one of such states, the PL of interlayer excitons is relatively amplified at increased optical excitation power due to reduced mobility, and the valley polarization of interlayer excitons is enhanced. The moiré superlattice of the TMDC heterobilayer presents an exciting platform to engineer interlayer excitons through the periodic correlated electron states.
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Affiliation(s)
- Shengnan Miao
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - Tianmeng Wang
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - Xiong Huang
- Department of Physics and Astronomy, University of California, Riverside, CA, USA
- Department of Materials Science and Engineering, University of California, Riverside, CA, USA
| | - Dongxue Chen
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, Sichuan, China
| | - Zhen Lian
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - Chong Wang
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Mark Blei
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Takashi Taniguchi
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Kenji Watanabe
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Sefaattin Tongay
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Zenghui Wang
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, Sichuan, China.
| | - Di Xiao
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Yong-Tao Cui
- Department of Physics and Astronomy, University of California, Riverside, CA, USA.
| | - Su-Fei Shi
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA.
- Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA.
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205
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Yin H, Xing K, Zhang Y, Dissanayake DMAS, Lu Z, Zhao H, Zeng Z, Yun JH, Qi DC, Yin Z. Periodic nanostructures: preparation, properties and applications. Chem Soc Rev 2021; 50:6423-6482. [PMID: 34100047 DOI: 10.1039/d0cs01146k] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Periodic nanostructures, a group of nanomaterials consisting of single or multiple nano units/components periodically arranged into ordered patterns (e.g., vertical and lateral superlattices), have attracted tremendous attention in recent years due to their extraordinary physical and chemical properties that offer a huge potential for a multitude of applications in energy conversion, electronic and optoelectronic applications. Recent advances in the preparation strategies of periodic nanostructures, including self-assembly, epitaxy, and exfoliation, have paved the way to rationally modulate their ferroelectricity, superconductivity, band gap and many other physical and chemical properties. For example, the recent discovery of superconductivity observed in "magic-angle" graphene superlattices has sparked intensive studies in new ways, creating superlattices in twisted 2D materials. Recent development in the various state-of-the-art preparations of periodic nanostructures has created many new ideas and findings, warranting a timely review. In this review, we discuss the current advances of periodic nanostructures, including their preparation strategies, property modulations and various applications.
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Affiliation(s)
- Hang Yin
- Research School of Chemistry, Australian National University, ACT 2601, Australia.
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206
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Huang X, Chen L, Tang S, Jiang C, Chen C, Wang H, Shen ZX, Wang H, Cui YT. Imaging Dual-Moiré Lattices in Twisted Bilayer Graphene Aligned on Hexagonal Boron Nitride Using Microwave Impedance Microscopy. NANO LETTERS 2021; 21:4292-4298. [PMID: 33949872 DOI: 10.1021/acs.nanolett.1c00601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Moiré superlattices (MSLs) formed in van der Waals materials have become a promising platform to realize novel two-dimensional electronic states. Angle-aligned trilayer structures can form two sets of MSLs which could potentially interfere. In this work, we directly image the moiré patterns in both monolayer and twisted bilayer graphene aligned on hexagonal boron nitride (hBN), using combined scanning microwave impedance microscopy and conductive atomic force microscopy. Correlation of the two techniques reveals the contrast mechanism for the achieved ultrahigh spatial resolution (<2 nm). We observe two sets of MSLs with different periodicities in the trilayer stack. The smaller MSL breaks the 6-fold rotational symmetry and exhibits abrupt discontinuities at the boundaries of the larger MSL. Using a rigid atomic-stacking model, we demonstrate that the hBN layer considerably modifies the MSL of twisted bilayer graphene. We further analyze its effect on the reciprocal space spectrum of the dual-moiré system.
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Affiliation(s)
- Xiong Huang
- Department of Physics and Astronomy, University of California, Riverside, California 92521, United States
- Department of Materials Science and Engineering, University of California, Riverside, California 92521, United States
| | - Lingxiu Chen
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou 221116, China
| | - Shujie Tang
- 2020 X-Lab, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Chengxin Jiang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Chen Chen
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Huishan Wang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Zhi-Xun Shen
- Department of Physics and Applied Physics, Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States
| | - Haomin Wang
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
| | - Yong-Tao Cui
- Department of Physics and Astronomy, University of California, Riverside, California 92521, United States
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207
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Sharpe AL, Fox EJ, Barnard AW, Finney J, Watanabe K, Taniguchi T, Kastner MA, Goldhaber-Gordon D. Evidence of Orbital Ferromagnetism in Twisted Bilayer Graphene Aligned to Hexagonal Boron Nitride. NANO LETTERS 2021; 21:4299-4304. [PMID: 33970644 DOI: 10.1021/acs.nanolett.1c00696] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We have previously reported ferromagnetism evinced by a large hysteretic anomalous Hall effect in twisted bilayer graphene (tBLG). Subsequent measurements of a quantized Hall resistance and small longitudinal resistance confirmed that this magnetic state is a Chern insulator. Here, we report that when tilting the sample in an external magnetic field, the ferromagnetism is highly anisotropic. Because spin-orbit coupling is weak in graphene, such anisotropy is unlikely to come from spin but rather favors theories in which the ferromagnetism is orbital. We know of no other case in which ferromagnetism has a purely orbital origin. For an applied in-plane field larger than 5 T, the out-of-plane magnetization is destroyed, suggesting a transition to a new phase.
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Affiliation(s)
- Aaron L Sharpe
- Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, United States
- Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Eli J Fox
- Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, United States
| | - Arthur W Barnard
- Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, United States
- Department of Physics and Department of Materials Science and Engineering, University of Washington, 302 Roberts Hall, Seattle, Washington 98195, United States
| | - Joe Finney
- Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, United States
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Marc A Kastner
- Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, United States
- Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - David Goldhaber-Gordon
- Stanford Institute for Materials and Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
- Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, United States
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208
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Marcellina E, Liu X, Hu Z, Fieramosca A, Huang Y, Du W, Liu S, Zhao J, Watanabe K, Taniguchi T, Xiong Q. Evidence for Moiré Trions in Twisted MoSe 2 Homobilayers. NANO LETTERS 2021; 21:4461-4468. [PMID: 33970625 DOI: 10.1021/acs.nanolett.1c01207] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Moiré superlattices of van der Waals structures offer a powerful platform for engineering band structure and quantum states. For instance, Moiré superlattices in magic-angle twisted bilayer graphene, ABC trilayer graphene have been shown to harbor correlated insulating and superconducting states, while in transition metal dichalcogenide (TMD) twisted bilayers, Moiré excitons have been identified. Here we show that the effects of a Moiré superlattice on the band structure are general: In TMD twisted bilayers, excitons and exciton complexes can be trapped in the superlattice in a manner analogous to ultracold bosonic or Fermionic atoms in optical lattices. Using twisted MoSe2 homobilayers as a model system, we present evidence for Moiré trions. Our results thus open possibilities for designer van der Waals structures hosting arrays of Fermionic or bosonic quasiparticles, which can be used to realize tunable many-body states crucial for quantum simulation and quantum information processing.
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Affiliation(s)
- Elizabeth Marcellina
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Xue Liu
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Zehua Hu
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Antonio Fieramosca
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Yuqing Huang
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Wei Du
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Sheng Liu
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Jiaxin Zhao
- School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Qihua Xiong
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P.R. China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, P.R. China
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209
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Lee JM, Oshikawa M, Cho GY. Non-Fermi Liquids in Conducting Two-Dimensional Networks. PHYSICAL REVIEW LETTERS 2021; 126:186601. [PMID: 34018806 DOI: 10.1103/physrevlett.126.186601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 04/01/2021] [Indexed: 06/12/2023]
Abstract
We explore the physics of novel fermion liquids emerging from conducting networks, where 1D metallic wires form a periodic 2D superstructure. Such structure naturally appears in marginally twisted bilayer graphenes, moire transition metal dichalcogenides, and also in some charge-density wave materials. For these network systems, we theoretically show that a remarkably wide variety of new non-Fermi liquids emerge and that these non-Fermi liquids can be classified by the characteristics of the junctions in networks. Using this, we calculate the electric conductivity of the non-Fermi liquids as a function of temperature, which show markedly different scaling behaviors than a regular 2D Fermi liquid.
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Affiliation(s)
- Jongjun M Lee
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang 37673, Korea
| | - Masaki Oshikawa
- Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
- Kavli Institute for the Physics and Mathematics of the Universe, Kashiwa 277-8583, Japan
- Trans-scale Quantum Science Institute, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Gil Young Cho
- Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang 37673, Korea
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210
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Li B, Geng J, Ai H, Kong Y, Bai H, Lo KH, Ng KW, Kawazoe Y, Pan H. Design of 2D materials - MSi 2C xN 4-x (M = Cr, Mo, and W; x = 1 and 2) - with tunable electronic and magnetic properties. NANOSCALE 2021; 13:8038-8048. [PMID: 33900351 DOI: 10.1039/d1nr00461a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Two-dimensional (2D) materials have attracted increasing interest in the past decades due to their unique physical and chemical properties for diverse applications. In this work, we present a first-principles design on a novel 2D family, MSi2CxN4-x (M = Cr, Mo, and W; x = 1 and 2), based on density-functional theory (DFT). We find that all MSi2CxN4-x monolayers are stable by investigating their mechanic, dynamic, and thermodynamic properties. Interestingly, we see that the alignment of magnetic moments can be tuned to achieve non-magnetism (NM), ferromagnetism (FM), anti-ferromagnetism (AFM) or paramagnetism (PM) by arranging the positions of carbon atoms in the 2D systems. Accordingly, their electronic properties can be controlled to obtain semiconductor, half-metal, or metal. The FM states in half-metallic 2D systems are contributed to the hole-mediated double exchange, while the AFM states are induced by super-exchange. Our findings show that the physical properties of 2D systems can be tuned by compositional and structural engineering, especially the layer of C atoms, which may provide guidance on the design and fabrication of novel 2D materials with projected properties for multi-functional applications.
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Affiliation(s)
- Bowen Li
- Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR, 999078, P.R. China.
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211
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Xu Y, Horn C, Zhu J, Tang Y, Ma L, Li L, Liu S, Watanabe K, Taniguchi T, Hone JC, Shan J, Mak KF. Creation of moiré bands in a monolayer semiconductor by spatially periodic dielectric screening. NATURE MATERIALS 2021; 20:645-649. [PMID: 33479527 DOI: 10.1038/s41563-020-00888-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Accepted: 11/24/2020] [Indexed: 06/12/2023]
Abstract
Moiré superlattices of two-dimensional van der Waals materials have emerged as a powerful platform for designing electronic band structures and discovering emergent physical phenomena. A key concept involves the creation of long-wavelength periodic potential and moiré bands in a crystal through interlayer electronic hybridization or atomic corrugation when two materials are overlaid. Here we demonstrate a new approach based on spatially periodic dielectric screening to create moiré bands in a monolayer semiconductor. This approach relies on reduced dielectric screening of the Coulomb interactions in monolayer semiconductors and their environmental dielectric-dependent electronic band structure. We observe optical transitions between moiré bands in monolayer WSe2 when it is placed close to small-angle-misaligned graphene on hexagonal boron nitride. The moiré bands are a result of long-range Coulomb interactions, which are strongly gate tunable, and can have versatile superlattice symmetries independent of the crystal lattice of the host material. Our result also demonstrates that monolayer semiconductors are sensitive local dielectric sensors.
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Affiliation(s)
- Yang Xu
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Connor Horn
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Jiacheng Zhu
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Yanhao Tang
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Liguo Ma
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Lizhong Li
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
| | - Song Liu
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - James C Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Jie Shan
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
| | - Kin Fai Mak
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, USA.
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA.
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212
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213
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Qiu D, Gong C, Wang S, Zhang M, Yang C, Wang X, Xiong J. Recent Advances in 2D Superconductors. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2006124. [PMID: 33768653 DOI: 10.1002/adma.202006124] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Revised: 10/22/2020] [Indexed: 06/12/2023]
Abstract
The emergence of superconductivity in 2D materials has attracted much attention and there has been rapid development in recent years because of their fruitful physical properties, such as high transition temperature (Tc ), continuous phase transition, and enhanced parallel critical magnetic field (Bc ). Tremendous efforts have been devoted to exploring different physical parameters to figure out the mechanisms behind the unexpected superconductivity phenomena, including adjusting the thickness of samples, fabricating various heterostructures, tuning the carrier density by electric field and chemical doping, and so on. Here, different types of 2D superconductivity with their unique characteristics are introduced, including the conventional Bardeen-Cooper-Schrieffer superconductivity in ultrathin films, high-Tc superconductivity in Fe-based and Cu-based 2D superconductors, unconventional superconductivity in newly discovered twist-angle bilayer graphene, superconductivity with enhanced Bc , and topological superconductivity. A perspective toward this field is then proposed based on academic knowledge from the recently reported literature. The aim is to provide researchers with a clear and comprehensive understanding about the newly developed 2D superconductivity and promote the development of this field much further.
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Affiliation(s)
- Dong Qiu
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Chuanhui Gong
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - SiShuang Wang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Miao Zhang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Chao Yang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Xianfu Wang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Jie Xiong
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
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214
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He F, Zhou Y, Ye Z, Cho SH, Jeong J, Meng X, Wang Y. Moiré Patterns in 2D Materials: A Review. ACS NANO 2021; 15:5944-5958. [PMID: 33769797 DOI: 10.1021/acsnano.0c10435] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Quantum materials have attracted much attention in recent years due to their exotic and incredible properties. Among them, van der Waals materials stand out due to their weak interlayer coupling, providing easy access to manipulating electrical and optical properties. Many fascinating electrical, optical, and magnetic properties have been reported in the moiré superlattices, such as unconventional superconductivity, photonic dispersion engineering, and ferromagnetism. In this review, we summarize the methods to prepare moiré superlattices in the van der Waals materials and focus on the current discoveries of moiré pattern-modified electrical properties, recent findings of atomic reconstruction, as well as some possible future directions in this field.
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Affiliation(s)
- Feng He
- State Key Laboratory on Tunable Laser Technology, School of Electronic and Information Engineering, Harbin Institute of Technology, Shenzhen 518055, China
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
- Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Yongjian Zhou
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Zefang Ye
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Sang-Hyeok Cho
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Jihoon Jeong
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Xianghai Meng
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Yaguo Wang
- Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
- Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
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215
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Zhao X, Qiao J, Chan SM, Li J, Dan J, Ning S, Zhou W, Quek SY, Pennycook SJ, Loh KP. Unveiling Atomic-Scale Moiré Features and Atomic Reconstructions in High-Angle Commensurately Twisted Transition Metal Dichalcogenide Homobilayers. NANO LETTERS 2021; 21:3262-3270. [PMID: 33749268 DOI: 10.1021/acs.nanolett.1c00563] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Twisting the angle between van der Waals stacked 2D layers has recently sparked great interest as a new strategy to tune the physical properties of the materials. The twist angle and associated strain profiles govern the electrical and optical properties of the twisted 2D materials, but their detailed atomic structures remain elusive. Herein, using combined atomic-resolution electron microscopy and density functional theory (DFT) calculations, we identified five unique types of moiré features in commensurately twisted 7a×7a transition metal dichalcogenide (TMD) bilayers. These stacking variants are distinguishable only when the moiré wavelength is short. Periodic lattice strain is observed in various commensurately twisted TMD bilayers. Assisted by Zernike polynomial as a hierarchical active-learning framework, a hexagon-shaped strain soliton network has been atomically unveiled in nearly commensurate twisted TMD bilayers. Unlike stacking-polytype-dependent properties in untwisted structures, the stacking variants have the same electronic structures that suggest twisted bilayer systems are invariant against interlayer gliding.
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Affiliation(s)
- Xiaoxu Zhao
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore
- Department of Chemistry, National University of Singapore, 3 Science Drive 3 117543, Singapore
| | - Jingsi Qiao
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
| | - Si Min Chan
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
| | - Jing Li
- Department of Chemistry, National University of Singapore, 3 Science Drive 3 117543, Singapore
| | - Jiadong Dan
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore
| | - Shoucong Ning
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore
| | - Wu Zhou
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Su Ying Quek
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
| | - Stephen John Pennycook
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore, 3 Science Drive 3 117543, Singapore
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216
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Han T, Yang J, Zhang Q, Wang L, Watanabe K, Taniguchi T, McEuen PL, Ju L. Accurate Measurement of the Gap of Graphene/h-BN Moiré Superlattice through Photocurrent Spectroscopy. PHYSICAL REVIEW LETTERS 2021; 126:146402. [PMID: 33891445 DOI: 10.1103/physrevlett.126.146402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/10/2021] [Indexed: 06/12/2023]
Abstract
Monolayer graphene aligned with hexagonal boron nitride (h-BN) develops a gap at the charge neutrality point (CNP). This gap has previously been extensively studied by electrical transport through thermal activation measurements. Here, we report the determination of the gap size at the CNP of graphene/h-BN superlattice through photocurrent spectroscopy study. We demonstrate two distinct measurement approaches to extract the gap size. A maximum of ∼14 meV gap is observed for devices with a twist angle of less than 1°. This value is significantly smaller than that obtained from thermal activation measurements, yet larger than the theoretically predicted single-particle gap. Our results suggest that lattice relaxation and moderate electron-electron interaction effects may enhance the CNP gap in graphene/h-BN superlattice.
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Affiliation(s)
- Tianyi Han
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jixiang Yang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Qihang Zhang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Lei Wang
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
- National Laboratory of Solid-State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Paul L McEuen
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Long Ju
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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217
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Andersen TI, Scuri G, Sushko A, De Greve K, Sung J, Zhou Y, Wild DS, Gelly RJ, Heo H, Bérubé D, Joe AY, Jauregui LA, Watanabe K, Taniguchi T, Kim P, Park H, Lukin MD. Excitons in a reconstructed moiré potential in twisted WSe 2/WSe 2 homobilayers. NATURE MATERIALS 2021; 20:480-487. [PMID: 33398121 DOI: 10.1038/s41563-020-00873-5] [Citation(s) in RCA: 60] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 11/11/2020] [Indexed: 06/12/2023]
Abstract
Moiré superlattices in twisted van der Waals materials have recently emerged as a promising platform for engineering electronic and optical properties. A major obstacle to fully understanding these systems and harnessing their potential is the limited ability to correlate direct imaging of the moiré structure with optical and electronic properties. Here we develop a secondary electron microscope technique to directly image stacking domains in fully functional van der Waals heterostructure devices. After demonstrating the imaging of AB/BA and ABA/ABC domains in multilayer graphene, we employ this technique to investigate reconstructed moiré patterns in twisted WSe2/WSe2 bilayers and directly correlate the increasing moiré periodicity with the emergence of two distinct exciton species in photoluminescence measurements. These states can be tuned individually through electrostatic gating and feature different valley coherence properties. We attribute our observations to the formation of an array of two intralayer exciton species that reside in alternating locations in the superlattice, and open up new avenues to realize tunable exciton arrays in twisted van der Waals heterostructures, with applications in quantum optoelectronics and explorations of novel many-body systems.
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Affiliation(s)
| | - Giovanni Scuri
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Andrey Sushko
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Kristiaan De Greve
- Department of Physics, Harvard University, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- imec, Leuven, Belgium
| | - Jiho Sung
- Department of Physics, Harvard University, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
| | - You Zhou
- Department of Physics, Harvard University, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
| | - Dominik S Wild
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Ryan J Gelly
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Hoseok Heo
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Damien Bérubé
- Department of Physics, California Institute of Technology, Pasadena, CA, USA
| | - Andrew Y Joe
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Luis A Jauregui
- Department of Physics, Harvard University, Cambridge, MA, USA
- Department of Physics and Astronomy, UC Irvine, Irvine, CA, 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
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, MA, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | - Hongkun Park
- Department of Physics, Harvard University, Cambridge, MA, USA.
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
| | - Mikhail D Lukin
- Department of Physics, Harvard University, Cambridge, MA, USA.
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218
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Lin KQ, Faria Junior PE, Bauer JM, Peng B, Monserrat B, Gmitra M, Fabian J, Bange S, Lupton JM. Twist-angle engineering of excitonic quantum interference and optical nonlinearities in stacked 2D semiconductors. Nat Commun 2021; 12:1553. [PMID: 33692339 PMCID: PMC7946969 DOI: 10.1038/s41467-021-21547-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 01/28/2021] [Indexed: 11/09/2022] Open
Abstract
Twist-engineering of the electronic structure in van-der-Waals layered materials relies predominantly on band hybridization between layers. Band-edge states in transition-metal-dichalcogenide semiconductors are localized around the metal atoms at the center of the three-atom layer and are therefore not particularly susceptible to twisting. Here, we report that high-lying excitons in bilayer WSe2 can be tuned over 235 meV by twisting, with a twist-angle susceptibility of 8.1 meV/°, an order of magnitude larger than that of the band-edge A-exciton. This tunability arises because the electronic states associated with upper conduction bands delocalize into the chalcogenide atoms. The effect gives control over excitonic quantum interference, revealed in selective activation and deactivation of electromagnetically induced transparency (EIT) in second-harmonic generation. Such a degree of freedom does not exist in conventional dilute atomic-gas systems, where EIT was originally established, and allows us to shape the frequency dependence, i.e., the dispersion, of the optical nonlinearity. Here, the authors report on the large twist-angle susceptibility of excitons involving upper conduction bands in transition metal dichalcogenide bilayers. These high-lying excitons couple with band-edge excitons, and give rise to nonlinear quantum-optical processes that become tuneable by twisting.
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Affiliation(s)
- Kai-Qiang Lin
- Department of Physics, University of Regensburg, Regensburg, Germany.
| | | | - Jonas M Bauer
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Bo Peng
- TCM Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Bartomeu Monserrat
- TCM Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK.,Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
| | - Martin Gmitra
- Department of Theoretical Physics and Astrophysics, Pavol Jozef Šafárik University, Košice, Slovakia
| | - Jaroslav Fabian
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Sebastian Bange
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - John M Lupton
- Department of Physics, University of Regensburg, Regensburg, Germany.
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219
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Angeli M, MacDonald AH. Γ valley transition metal dichalcogenide moiré bands. Proc Natl Acad Sci U S A 2021; 118:e2021826118. [PMID: 33658375 PMCID: PMC7958387 DOI: 10.1073/pnas.2021826118] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The valence band maxima of most group VI transition metal dichalcogenide thin films remain at the Γ point all of the way from bulk to bilayer. In this paper, we develop a continuum theory of the moiré minibands that are formed in the valence bands of Γ-valley homobilayers by a small relative twist. Our effective theory is benchmarked against large-scale ab initio electronic structure calculations that account for lattice relaxation. As a consequence of an emergent [Formula: see text] symmetry, we find that low-energy Γ-valley moiré holes differ qualitatively from their K-valley counterparts addressed previously; in energetic order, the first three bands realize 1) a single-orbital model on a honeycomb lattice, 2) a two-orbital model on a honeycomb lattice, and 3) a single-orbital model on a kagome lattice.
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Affiliation(s)
- Mattia Angeli
- International School for Advanced Studies, I-34136 Trieste, Italy;
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220
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Liu Y, Holder T, Yan B. Chirality-Induced Giant Unidirectional Magnetoresistance in Twisted Bilayer Graphene. Innovation (N Y) 2021; 2:100085. [PMID: 33738460 PMCID: PMC7938422 DOI: 10.1016/j.xinn.2021.100085] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 01/18/2021] [Indexed: 11/27/2022] Open
Abstract
Twisted bilayer graphene (TBG) exhibits fascinating correlation-driven phenomena like the superconductivity and Mott insulating state, with flat bands and a chiral lattice structure. We find by quantum-transport calculations that the chirality leads to a giant unidirectional magnetoresistance (UMR) in TBG, where the unidirectionality refers to the resistance change under the reversal of the direction of current or magnetic field. We point out that flat bands significantly enhance this effect. The UMR increases quickly upon reducing the twist angle, and reaches about 20% for an angle of 1.5° in a 10 T in-plane magnetic field. We propose the band structure topology (asymmetry), which leads to a direction-sensitive mean free path, as a useful way to anticipate the UMR effect. The UMR provides a probe for chirality and band flatness in the twisted bilayers. Twisted bilayer graphene (TBG) was recently discovered to exhibit fascinating phenomena like the superconductivity and Mott insulating state TBG's chirality leads to a unidirectional magnetoresistance (UMR), where magnetoresistance is lower in a chirality-dependent direction. The flat bands of TBG enhance the UMR dramatically The giant UMR represents diode-like current rectification and can convert radiation (e.g., terahertz) into currents for energy-harvesting and photodetection
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Affiliation(s)
- Yizhou Liu
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Tobias Holder
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Binghai Yan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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221
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Liu B, Xian L, Mu H, Zhao G, Liu Z, Rubio A, Wang ZF. Higher-Order Band Topology in Twisted Moiré Superlattice. PHYSICAL REVIEW LETTERS 2021; 126:066401. [PMID: 33635687 DOI: 10.1103/physrevlett.126.066401] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 01/21/2021] [Indexed: 06/12/2023]
Abstract
The two-dimensional (2D) twisted bilayer materials with van der Waals coupling have ignited great research interests, paving a new way to explore the emergent quantum phenomena by twist degree of freedom. Generally, with the decreasing of twist angle, the enhanced interlayer coupling will gradually flatten the low-energy bands and isolate them by two high-energy gaps at zero and full filling, respectively. Although the correlation and topological physics in the low-energy flat bands have been intensively studied, little information is available for these two emerging gaps. In this Letter, we predict a 2D second-order topological insulator (SOTI) for twisted bilayer graphene and twisted bilayer boron nitride in both zero and full filling gaps. Employing a tight-binding Hamiltonian based on first-principles calculations, three unique fingerprints of 2D SOTI are identified, that is, nonzero bulk topological index, gapped topological edge state, and in-gap topological corner state. Most remarkably, the 2D SOTI exists in a wide range of commensurate twist angles, which is robust to microscopic structure disorder and twist center, greatly facilitating the possible experimental measurement. Our results not only extend the higher-order band topology to massless and massive twisted moiré superlattice, but also demonstrate the importance of high-energy bands for fully understanding the nontrivial electronics.
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Affiliation(s)
- Bing Liu
- Hefei National Laboratory for Physical Sciences at the Microscale, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Lede Xian
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Haimen Mu
- Hefei National Laboratory for Physical Sciences at the Microscale, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Gan Zhao
- Hefei National Laboratory for Physical Sciences at the Microscale, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Zhao Liu
- Hefei National Laboratory for Physical Sciences at the Microscale, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany
- Center for Computational Quantum Physics, Simons Foundation Flatiron Institute, New York, New York 10010, USA
- Nano-Bio Spectroscopy Group, Departamento de Fisica de Materiales, Universidad del País Vasco, UPV/EHU-20018 San Sebastián, Spain
| | - Z F Wang
- Hefei National Laboratory for Physical Sciences at the Microscale, CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
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222
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Park JM, Cao Y, Watanabe K, Taniguchi T, Jarillo-Herrero P. Tunable strongly coupled superconductivity in magic-angle twisted trilayer graphene. Nature 2021; 590:249-255. [DOI: 10.1038/s41586-021-03192-0] [Citation(s) in RCA: 227] [Impact Index Per Article: 75.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 01/05/2021] [Indexed: 12/24/2022]
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223
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Choi J, Florian M, Steinhoff A, Erben D, Tran K, Kim DS, Sun L, Quan J, Claassen R, Majumder S, Hollingsworth JA, Taniguchi T, Watanabe K, Ueno K, Singh A, Moody G, Jahnke F, Li X. Twist Angle-Dependent Interlayer Exciton Lifetimes in van der Waals Heterostructures. PHYSICAL REVIEW LETTERS 2021; 126:047401. [PMID: 33576642 DOI: 10.1103/physrevlett.126.047401] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 11/13/2020] [Accepted: 12/04/2020] [Indexed: 06/12/2023]
Abstract
In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are formed and subject to both vertical and lateral confinement. We investigate how a unique control knob, the twist angle between the two monolayers, can be used to control the exciton dynamics. We observe that the interlayer exciton lifetimes in MoSe_{2}/WSe_{2} twisted bilayers (TBLs) change by one order of magnitude when the twist angle is varied from 1° to 3.5°. Using a low-energy continuum model, we theoretically separate two leading mechanisms that influence interlayer exciton radiative lifetimes. The shift to indirect transitions in the momentum space with an increasing twist angle and the energy modulation from the moiré potential both have a significant impact on interlayer exciton lifetimes. We further predict distinct temperature dependence of interlayer exciton lifetimes in TBLs with different twist angles, which is partially validated by experiments. While many recent studies have highlighted how the twist angle in a vdW TBL can be used to engineer the ground states and quantum phases due to many-body interaction, our studies explore its role in controlling the dynamics of optically excited states, thus, expanding the conceptual applications of "twistronics".
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Affiliation(s)
- Junho Choi
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Matthias Florian
- Institute for Theoretical Physics, University of Bremen, 28334 Bremen, Germany
| | - Alexander Steinhoff
- Institute for Theoretical Physics, University of Bremen, 28334 Bremen, Germany
| | - Daniel Erben
- Institute for Theoretical Physics, University of Bremen, 28334 Bremen, Germany
| | - Kha Tran
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Dong Seob Kim
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Liuyang Sun
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Jiamin Quan
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Robert Claassen
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Somak Majumder
- Materials Physics & Applications Division: Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Jennifer A Hollingsworth
- Materials Physics & Applications Division: Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Keiji Ueno
- Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570, Japan
| | - Akshay Singh
- Department of Physics, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | - Galan Moody
- Department of Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California 93106, USA
| | - Frank Jahnke
- Institute for Theoretical Physics, University of Bremen, 28334 Bremen, Germany
| | - Xiaoqin Li
- Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712, USA
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224
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Excitonic density wave and spin-valley superfluid in bilayer transition metal dichalcogenide. Nat Commun 2021; 12:642. [PMID: 33510138 PMCID: PMC7843647 DOI: 10.1038/s41467-020-20802-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Accepted: 12/13/2020] [Indexed: 11/10/2022] Open
Abstract
Artificial moiré superlattices in 2d van der Waals heterostructures are a new venue for realizing and controlling correlated electronic phenomena. Recently, twisted bilayer WSe2 emerged as a new robust moiré system hosting a correlated insulator at moiré half-filling over a range of twist angle. In this work, we present a theory of this insulating state as an excitonic density wave due to intervalley electron–hole pairing. We show that exciton condensation is strongly enhanced by a van Hove singularity near the Fermi level. Our theory explains the remarkable sensitivity of the insulating gap to the vertical electric field. In contrast, the gap is weakly reduced by a perpendicular magnetic field, with quadratic dependence at low field. The different responses to electric and magnetic field can be understood in terms of pair-breaking versus non-pair-breaking effects in a BCS analog of the system. We further predict superfluid spin transport in this electrical insulator, which can be detected by optical spin injection and spatial-temporal imaging. A correlated insulator has recently been observed in twisted bilayer WSe2 moiré superlattices. Here, Bi and Fu present a theory and predict the insulating state to be an excitonic density wave as well as a spin-valley superfluid, which can be tested by optical pump-probe experiments.
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225
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Soubelet P, Klein J, Wierzbowski J, Silvioli R, Sigger F, Stier AV, Gallo K, Finley JJ. Charged Exciton Kinetics in Monolayer MoSe 2 near Ferroelectric Domain Walls in Periodically Poled LiNbO 3. NANO LETTERS 2021; 21:959-966. [PMID: 33428406 DOI: 10.1021/acs.nanolett.0c03810] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Monolayer semiconducting transition metal dichalcogenides are a strongly emergent platform for exploring quantum phenomena in condensed matter, building novel optoelectronic devices with enhanced functionalities. Because of their atomic thickness, their excitonic optical response is highly sensitive to their dielectric environment. In this work, we explore the optical properties of monolayer thick MoSe2 straddling domain wall boundaries in periodically poled LiNbO3. Spatially resolved photoluminescence experiments reveal spatial sorting of charge and photogenerated neutral and charged excitons across the boundary. Our results reveal evidence for extremely large in-plane electric fields of ≃4000 kV/cm at the domain wall whose effect is manifested in exciton dissociation and routing of free charges and trions toward oppositely poled domains and a nonintuitive spatial intensity dependence. By modeling our result using drift-diffusion and continuity equations, we obtain excellent qualitative agreement with our observations and have explained the observed spatial luminescence modulation using realistic material parameters.
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Affiliation(s)
- Pedro Soubelet
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
| | - Julian Klein
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Jakob Wierzbowski
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
| | - Riccardo Silvioli
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
| | - Florian Sigger
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
| | - Andreas V Stier
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
| | - Katia Gallo
- Department of Applied Physics, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - Jonathan J Finley
- Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748, Garching, Germany
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226
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Kerelsky A, Rubio-Verdú C, Xian L, Kennes DM, Halbertal D, Finney N, Song L, Turkel S, Wang L, Watanabe K, Taniguchi T, Hone J, Dean C, Basov DN, Rubio A, Pasupathy AN. Moiréless correlations in ABCA graphene. Proc Natl Acad Sci U S A 2021; 118:e2017366118. [PMID: 33468646 PMCID: PMC7848726 DOI: 10.1073/pnas.2017366118] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Atomically thin van der Waals materials stacked with an interlayer twist have proven to be an excellent platform toward achieving gate-tunable correlated phenomena linked to the formation of flat electronic bands. In this work we demonstrate the formation of emergent correlated phases in multilayer rhombohedral graphene--a simple material that also exhibits a flat electronic band edge but without the need of having a moiré superlattice induced by twisted van der Waals layers. We show that two layers of bilayer graphene that are twisted by an arbitrary tiny angle host large (micrometer-scale) regions of uniform rhombohedral four-layer (ABCA) graphene that can be independently studied. Scanning tunneling spectroscopy reveals that ABCA graphene hosts an unprecedentedly sharp van Hove singularity of 3-5-meV half-width. We demonstrate that when this van Hove singularity straddles the Fermi level, a correlated many-body gap emerges with peak-to-peak value of 9.5 meV at charge neutrality. Mean-field theoretical calculations for model with short-ranged interactions indicate that two primary candidates for the appearance of this broken symmetry state are a charge-transfer excitonic insulator and a ferrimagnet. Finally, we show that ABCA graphene hosts surface topological helical edge states at natural interfaces with ABAB graphene which can be turned on and off with gate voltage, implying that small-angle twisted double-bilayer graphene is an ideal programmable topological quantum material.
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Affiliation(s)
| | | | - Lede Xian
- Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany
- Frontier Research Center, Songshan Lake Materials Laboratory, 523808 Dongguan, Guangdong, China
| | - Dante M Kennes
- Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany
- Institut für Theorie der Statistischen Physik, Rheinisch-Westfälische Technische Hochschule Aachen University, 52056 Aachen, Germany
- Jülich Aachen Research Alliance-Fundamentals of Future Information Technology, 52056 Aachen, Germany
| | - Dorri Halbertal
- Department of Physics, Columbia University, New York, NY 10027
| | - Nathan Finney
- Department of Mechanical Engineering, Columbia University, New York, NY 10027
| | - Larry Song
- Department of Physics, Columbia University, New York, NY 10027
| | - Simon Turkel
- Department of Physics, Columbia University, New York, NY 10027
| | - Lei Wang
- Department of Physics, Columbia University, New York, NY 10027
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, 305-0044 Tsukuba, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, 305-0044 Tsukuba, Japan
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY 10027
| | - Cory Dean
- Department of Physics, Columbia University, New York, NY 10027
| | - Dmitri N Basov
- Department of Physics, Columbia University, New York, NY 10027
| | - Angel Rubio
- Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany;
- Center for Computational Quantum Physics, The Flatiron Institute, New York, NY 10010
- Nano-Bio Spectroscopy Group, Departamento de Fisica de Materiales, Universidad del País Vasco, 20018 San Sebastian, Spain
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227
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Peri V, Song ZD, Bernevig BA, Huber SD. Fragile Topology and Flat-Band Superconductivity in the Strong-Coupling Regime. PHYSICAL REVIEW LETTERS 2021; 126:027002. [PMID: 33512222 DOI: 10.1103/physrevlett.126.027002] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Accepted: 12/11/2020] [Indexed: 06/12/2023]
Abstract
In flat bands, superconductivity can lead to surprising transport effects. The superfluid "mobility", in the form of the superfluid weight D_{s}, does not draw from the curvature of the band but has a purely band-geometric origin. In a mean-field description, a nonzero Chern number or fragile topology sets a lower bound for D_{s}, which, via the Berezinskii-Kosterlitz-Thouless mechanism, might explain the relatively high superconducting transition temperature measured in magic-angle twisted bilayer graphene (MATBG). For fragile topology, relevant for the bilayer system, the fate of this bound for finite temperature and beyond the mean-field approximation remained, however, unclear. Here, we numerically use exact Monte Carlo simulations to study an attractive Hubbard model in flat bands with topological properties akin to those of MATBG. We find a superconducting phase transition with a critical temperature that scales linearly with the interaction strength. Then, we investigate the robustness of the superconducting state to the addition of trivial bands that may or may not trivialize the fragile topology. Our results substantiate the validity of the topological bound beyond the mean-field regime and further stress the importance of fragile topology for flat-band superconductivity.
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Affiliation(s)
- Valerio Peri
- Institute for Theoretical Physics, ETH Zurich, 8093 Zürich, Switzerland
| | - Zhi-Da Song
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - B Andrei Bernevig
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Sebastian D Huber
- Institute for Theoretical Physics, ETH Zurich, 8093 Zürich, Switzerland
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228
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Yang Y, Li J, Yin J, Xu S, Mullan C, Taniguchi T, Watanabe K, Geim AK, Novoselov KS, Mishchenko A. In situ manipulation of van der Waals heterostructures for twistronics. SCIENCE ADVANCES 2020; 6:eabd3655. [PMID: 33277256 PMCID: PMC7717928 DOI: 10.1126/sciadv.abd3655] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 10/22/2020] [Indexed: 05/30/2023]
Abstract
In van der Waals heterostructures, electronic bands of two-dimensional (2D) materials, their nontrivial topology, and electron-electron interactions can be markedly changed by a moiré pattern induced by twist angles between different layers. This process is referred to as twistronics, where the tuning of twist angle can be realized through mechanical manipulation of 2D materials. Here, we demonstrate an experimental technique that can achieve in situ dynamical rotation and manipulation of 2D materials in van der Waals heterostructures. Using this technique, we fabricated heterostructures where graphene is perfectly aligned with both top and bottom encapsulating layers of hexagonal boron nitride. Our technique enables twisted 2D material systems in one single stack with dynamically tunable optical, mechanical, and electronic properties.
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Affiliation(s)
- Yaping Yang
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Jidong Li
- State Key Laboratory of Mechanics and Control of Mechanical Structures and MOE Key Laboratory for Intelligent Nano Materials and Devices, College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
| | - Jun Yin
- State Key Laboratory of Mechanics and Control of Mechanical Structures and MOE Key Laboratory for Intelligent Nano Materials and Devices, College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
| | - Shuigang Xu
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Ciaran Mullan
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Andre K Geim
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Konstantin S Novoselov
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Centre for Advanced 2D Materials, National University of Singapore, 117546, Singapore
| | - Artem Mishchenko
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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229
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Andrei EY, MacDonald AH. Graphene bilayers with a twist. NATURE MATERIALS 2020; 19:1265-1275. [PMID: 33208935 DOI: 10.1038/s41563-020-00840-0] [Citation(s) in RCA: 160] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 09/24/2020] [Indexed: 05/02/2023]
Abstract
Near a magic twist angle, bilayer graphene transforms from a weakly correlated Fermi liquid to a strongly correlated two-dimensional electron system with properties that are extraordinarily sensitive to carrier density and to controllable environmental factors such as the proximity of nearby gates and twist-angle variation. Among other phenomena, magic-angle twisted bilayer graphene hosts superconductivity, interaction-induced insulating states, magnetism, electronic nematicity, linear-in-temperature low-temperature resistivity and quantized anomalous Hall states. We highlight some key research results in this field, point to important questions that remain open and comment on the place of magic-angle twisted bilayer graphene in the strongly correlated quantum matter world.
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Affiliation(s)
- Eva Y Andrei
- Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ, USA.
| | - Allan H MacDonald
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
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230
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Zhu J, Su JJ, MacDonald AH. Voltage-Controlled Magnetic Reversal in Orbital Chern Insulators. PHYSICAL REVIEW LETTERS 2020; 125:227702. [PMID: 33315456 DOI: 10.1103/physrevlett.125.227702] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Revised: 08/28/2020] [Accepted: 10/21/2020] [Indexed: 06/12/2023]
Abstract
Chern insulator ferromagnets are characterized by a quantized anomalous Hall effect and have so far been identified experimentally in magnetically doped topological insulator thin films and in bilayer graphene moiré superlattices. We classify Chern insulator ferromagnets as either spin or orbital, depending on whether the orbital magnetization results from spontaneous spin polarization combined with spin-orbit interactions, as in the magnetically doped topological insulator case, or directly from spontaneous orbital currents, as in the moiré superlattice case. We argue that, in a given magnetic state, characterized, for example, by the sign of the anomalous Hall effect, the magnetization of an orbital Chern insulator will often have opposite signs for weak n and weak p electrostatic or chemical doping. This property enables pure electrical switching of a magnetic state in the presence of a fixed magnetic field.
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Affiliation(s)
- Jihang Zhu
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Jung-Jung Su
- Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan
| | - A H MacDonald
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
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231
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Zheng Z, Ma Q, Bi Z, de la Barrera S, Liu MH, Mao N, Zhang Y, Kiper N, Watanabe K, Taniguchi T, Kong J, Tisdale WA, Ashoori R, Gedik N, Fu L, Xu SY, Jarillo-Herrero P. Unconventional ferroelectricity in moiré heterostructures. Nature 2020; 588:71-76. [DOI: 10.1038/s41586-020-2970-9] [Citation(s) in RCA: 77] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 10/07/2020] [Indexed: 11/09/2022]
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232
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Correlated insulating states at fractional fillings of moiré superlattices. Nature 2020; 587:214-218. [PMID: 33177668 DOI: 10.1038/s41586-020-2868-6] [Citation(s) in RCA: 145] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Accepted: 09/03/2020] [Indexed: 11/08/2022]
Abstract
Quantum particles on a lattice with competing long-range interactions are ubiquitous in physics; transition metal oxides1,2, layered molecular crystals3 and trapped-ion arrays4 are a few examples. In the strongly interacting regime, these systems often show a rich variety of quantum many-body ground states that challenge theory2. The emergence of transition metal dichalcogenide moiré superlattices provides a highly controllable platform in which to study long-range electronic correlations5-12. Here we report an observation of nearly two dozen correlated insulating states at fractional fillings of tungsten diselenide/tungsten disulfide moiré superlattices. This finding is enabled by a new optical sensing technique that is based on the sensitivity to the dielectric environment of the exciton excited states in a single-layer semiconductor of tungsten diselenide. The cascade of insulating states shows an energy ordering that is nearly symmetric about a filling factor of half a particle per superlattice site. We propose a series of charge-ordered states at commensurate filling fractions that range from generalized Wigner crystals7 to charge density waves. Our study lays the groundwork for using moiré superlattices to simulate a wealth of quantum many-body problems that are described by the two-dimensional extended Hubbard model3,13,14 or spin models with long-range charge-charge and exchange interactions15,16.
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233
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Chu Z, Regan EC, Ma X, Wang D, Xu Z, Utama MIB, Yumigeta K, Blei M, Watanabe K, Taniguchi T, Tongay S, Wang F, Lai K. Nanoscale Conductivity Imaging of Correlated Electronic States in WSe_{2}/WS_{2} Moiré Superlattices. PHYSICAL REVIEW LETTERS 2020; 125:186803. [PMID: 33196228 DOI: 10.1103/physrevlett.125.186803] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 10/02/2020] [Indexed: 06/11/2023]
Abstract
We report the nanoscale conductivity imaging of correlated electronic states in angle-aligned WSe_{2}/WS_{2} heterostructures using microwave impedance microscopy. The noncontact microwave probe allows us to observe the Mott insulating state with one hole per moiré unit cell that persists for temperatures up to 150 K, consistent with other characterization techniques. In addition, we identify for the first time a Mott insulating state at one electron per moiré unit cell. Appreciable inhomogeneity of the correlated states is directly visualized in the heterobilayer region, indicative of local disorders in the moiré superlattice potential or electrostatic doping. Our work provides important insights on 2D moiré systems down to the microscopic level.
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Affiliation(s)
- Zhaodong Chu
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Emma C Regan
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, California 94720, USA
- Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Xuejian Ma
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Danqing Wang
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, California 94720, USA
- Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Zifan Xu
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - M Iqbal Bakti Utama
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, USA
| | - Kentaro Yumigeta
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA
| | - Mark Blei
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Sefaattin Tongay
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA
| | - Feng Wang
- Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
- Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Kavli Energy NanoSciences Institute at University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Keji Lai
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
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234
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Sung J, Zhou Y, Scuri G, Zólyomi V, Andersen TI, Yoo H, Wild DS, Joe AY, Gelly RJ, Heo H, Magorrian SJ, Bérubé D, Valdivia AMM, Taniguchi T, Watanabe K, Lukin MD, Kim P, Fal'ko VI, Park H. Broken mirror symmetry in excitonic response of reconstructed domains in twisted MoSe 2/MoSe 2 bilayers. NATURE NANOTECHNOLOGY 2020; 15:750-754. [PMID: 32661373 DOI: 10.1038/s41565-020-0728-z] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 06/03/2020] [Indexed: 05/27/2023]
Abstract
Van der Waals heterostructures obtained via stacking and twisting have been used to create moiré superlattices1, enabling new optical and electronic properties in solid-state systems. Moiré lattices in twisted bilayers of transition metal dichalcogenides (TMDs) result in exciton trapping2-5, host Mott insulating and superconducting states6 and act as unique Hubbard systems7-9 whose correlated electronic states can be detected and manipulated optically. Structurally, these twisted heterostructures feature atomic reconstruction and domain formation10-14. However, due to the nanoscale size of moiré domains, the effects of atomic reconstruction on the electronic and excitonic properties have not been systematically investigated. Here we use near-0°-twist-angle MoSe2/MoSe2 bilayers with large rhombohedral AB/BA domains15 to directly probe the excitonic properties of individual domains with far-field optics. We show that this system features broken mirror/inversion symmetry, with the AB and BA domains supporting interlayer excitons with out-of-plane electric dipole moments in opposite directions. The dipole orientation of ground-state Γ-K interlayer excitons can be flipped with electric fields, while higher-energy K-K interlayer excitons undergo field-asymmetric hybridization with intralayer K-K excitons. Our study reveals the impact of crystal symmetry on TMD excitons and points to new avenues for realizing topologically non-trivial systems16,17, exotic metasurfaces18, collective excitonic phases19 and quantum emitter arrays20,21 via domain-pattern engineering.
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Affiliation(s)
- Jiho Sung
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - You Zhou
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Giovanni Scuri
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Viktor Zólyomi
- National Graphene Institute, University of Manchester, Manchester, UK
- Hartree Centre, STFC Daresbury Laboratory, Daresbury, UK
| | | | - Hyobin Yoo
- Department of Physics, Harvard University, Cambridge, MA, USA
- Department of Physics, Sogang University, Seoul, Republic of Korea
| | - Dominik S Wild
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Andrew Y Joe
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Ryan J Gelly
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Hoseok Heo
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | | | - Damien Bérubé
- Department of Physics, California Institute of Technology, Pasadena, CA, USA
| | - Andrés M Mier Valdivia
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | | | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | - Mikhail D Lukin
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, MA, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | - Vladimir I Fal'ko
- National Graphene Institute, University of Manchester, Manchester, UK.
- Henry Royce Institute for Advanced Materials, University of Manchester, Manchester, UK.
| | - Hongkun Park
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
- Department of Physics, Harvard University, Cambridge, MA, USA.
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235
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Liu J. Two monolayers is greater than a bilayer. NATURE MATERIALS 2020; 19:824-826. [PMID: 32704136 DOI: 10.1038/s41563-020-0733-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Affiliation(s)
- Junwei Liu
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
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