1
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Chakraborti H, Gorini C, Knothe A, Liu MH, Makk P, Parmentier FD, Perconte D, Richter K, Roulleau P, Sacépé B, Schönenberger C, Yang W. Electron wave and quantum optics in graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:393001. [PMID: 38697131 DOI: 10.1088/1361-648x/ad46bc] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2023] [Accepted: 05/01/2024] [Indexed: 05/04/2024]
Abstract
In the last decade, graphene has become an exciting platform for electron optical experiments, in some aspects superior to conventional two-dimensional electron gases (2DEGs). A major advantage, besides the ultra-large mobilities, is the fine control over the electrostatics, which gives the possibility of realising gap-less and compact p-n interfaces with high precision. The latter host non-trivial states,e.g., snake states in moderate magnetic fields, and serve as building blocks of complex electron interferometers. Thanks to the Dirac spectrum and its non-trivial Berry phase, the internal (valley and sublattice) degrees of freedom, and the possibility to tailor the band structure using proximity effects, such interferometers open up a completely new playground based on novel device architectures. In this review, we introduce the theoretical background of graphene electron optics, fabrication methods used to realise electron-optical devices, and techniques for corresponding numerical simulations. Based on this, we give a comprehensive review of ballistic transport experiments and simple building blocks of electron optical devices both in single and bilayer graphene, highlighting the novel physics that is brought in compared to conventional 2DEGs. After describing the different magnetic field regimes in graphene p-n junctions and nanostructures, we conclude by discussing the state of the art in graphene-based Mach-Zender and Fabry-Perot interferometers.
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Affiliation(s)
| | - Cosimo Gorini
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette, France
| | - Angelika Knothe
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Ming-Hao Liu
- Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University, Tainan 70101, Taiwan
| | - Péter Makk
- Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3., Budapest H-1111, Hungary
- MTA-BME Correlated van der Waals Structures Momentum Research Group, Műegyetem rkp. 3., Budapest H-1111, Hungary
| | | | - David Perconte
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
| | - Klaus Richter
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Preden Roulleau
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette, France
| | - Benjamin Sacépé
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
| | | | - Wenmin Yang
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
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2
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Klanurak I, Watanabe K, Taniguchi T, Chatraphorn S, Taychatanapat T. Probing the Anisotropic Fermi Surface in Tetralayer Graphene via Transverse Magnetic Focusing. NANO LETTERS 2024; 24:6330-6336. [PMID: 38723237 PMCID: PMC11140744 DOI: 10.1021/acs.nanolett.4c01133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Revised: 05/04/2024] [Accepted: 05/08/2024] [Indexed: 05/15/2024]
Abstract
Bernal-stacked tetralayer graphene (4LG) exhibits intriguing low-energy properties, featuring two massive sub-bands and showcasing diverse features of topologically distinct, anisotropic Fermi surfaces, including Lifshitz transitions and trigonal warping. Here, we study the influence of the band structure on electron dynamics within 4LG using transverse magnetic focusing. Our analysis reveals two distinct focusing peaks corresponding to the two sub-bands. Furthermore, we uncover a pronounced dependence of the focusing spectra on crystal orientations, indicative of an anisotropic Fermi surface. Utilizing the semiclassical model, we attribute this orientation-dependent behavior to the trigonal warping of the band structure. This phenomenon leads to variations in electron trajectories based on crystal orientation. Our findings not only enhance our understanding of the dynamics of electrons in 4LG but also offer a promising method for probing anisotropic Fermi surfaces in other materials.
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Affiliation(s)
- Illias Klanurak
- Department
of Physics, Faculty of Science, Chulalongkorn
University, Patumwan, Bangkok 10330, Thailand
| | - Kenji Watanabe
- Research
Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research
Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Sojiphong Chatraphorn
- Department
of Physics, Faculty of Science, Chulalongkorn
University, Patumwan, Bangkok 10330, Thailand
| | - Thiti Taychatanapat
- Department
of Physics, Faculty of Science, Chulalongkorn
University, Patumwan, Bangkok 10330, Thailand
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3
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Shilov AL, Kashchenko MA, Pantaleón Peralta PA, Wang Y, Kravtsov M, Kudriashov A, Zhan Z, Taniguchi T, Watanabe K, Slizovskiy S, Novoselov KS, Fal'ko VI, Guinea F, Bandurin DA. High-Mobility Compensated Semimetals, Orbital Magnetization, and Umklapp Scattering in Bilayer Graphene Moiré Superlattices. ACS NANO 2024; 18:11769-11777. [PMID: 38648369 DOI: 10.1021/acsnano.3c13212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
Twist-controlled moiré superlattices (MSs) have emerged as a versatile platform for realizing artificial systems with complex electronic spectra. The combination of Bernal-stacked bilayer graphene (BLG) and hexagonal boron nitride (hBN) can give rise to an interesting MS, which has recently featured a set of unexpected behaviors, such as unconventional ferroelectricity and the electronic ratchet effect. Yet, the understanding of the electronic properties of BLG/hBN MS has, at present, remained fairly limited. Here, we combine magneto-transport and low-energy sub-THz excitation to gain insights into the properties of this MS. We demonstrate that the alignment between BLG and hBN crystal lattices results in the emergence of compensated semimetals at some integer fillings of the moiré bands, separated by van Hove singularities where the Lifshitz transition occurs. A particularly pronounced semimetal develops when eight holes reside in the moiré unit cell, where coexisting high-mobility electron and hole systems feature strong magnetoresistance reaching 2350% already at B = 0.25 T. Next, by measuring the THz-driven Nernst effect in remote bands, we observe valley splitting, indicating an orbital magnetization characterized by a strongly enhanced effective gv-factor of 340. Finally, using THz photoresistance measurements, we show that the high-temperature conductivity of the BLG/hBN MS is limited by electron-electron umklapp processes. Our multifaceted analysis introduces THz-driven magnetotransport as a convenient tool to probe the band structure and interaction effects in van der Waals materials and provides a comprehensive understanding of the BLG/hBN MS.
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Affiliation(s)
- Artur L Shilov
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
| | - Mikhail A Kashchenko
- Programmable Functional Materials Lab, Center for Neurophysics and Neuromorphic Technologies, Moscow 127495, Russia
| | | | - Yibo Wang
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Mikhail Kravtsov
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Andrei Kudriashov
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Zhen Zhan
- IMDEA Nanoscience, Faraday 9, Madrid 28015, Spain
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - Sergey Slizovskiy
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, U.K
| | - Kostya S Novoselov
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117575, Singapore
| | - Vladimir I Fal'ko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, U.K
| | - Francisco Guinea
- IMDEA Nanoscience, Faraday 9, Madrid 28015, Spain
- Donostia International Physics Center, Paseo Manuel de Lardizábal 4, San Sebastián 20018, Spain
| | - Denis A Bandurin
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
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4
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de Vries F, Slizovskiy S, Tomić P, Krishna Kumar R, Garcia-Ruiz A, Zheng G, Portolés E, Ponomarenko LA, Geim AK, Watanabe K, Taniguchi T, Fal’ko V, Ensslin K, Ihn T, Rickhaus P. Kagome Quantum Oscillations in Graphene Superlattices. NANO LETTERS 2024; 24:601-606. [PMID: 38180909 PMCID: PMC10797620 DOI: 10.1021/acs.nanolett.3c03524] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 12/17/2023] [Accepted: 12/19/2023] [Indexed: 01/07/2024]
Abstract
Electronic spectra of solids subjected to a magnetic field are often discussed in terms of Landau levels and Hofstadter-butterfly-style Brown-Zak minibands manifested by magneto-oscillations in two-dimensional electron systems. Here, we present the semiclassical precursors of these quantum magneto-oscillations which appear in graphene superlattices at low magnetic field near the Lifshitz transitions and persist at elevated temperatures. These oscillations originate from Aharonov-Bohm interference of electron waves following open trajectories that belong to a kagome-shaped network of paths characteristic for Lifshitz transitions in the moire superlattice minibands of twistronic graphenes.
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Affiliation(s)
| | - Sergey Slizovskiy
- National
Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Department
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, United Kingdom
| | - Petar Tomić
- Laboratory
for Solid State Physics, ETH Zürich, Zürich CH-8093, Switzerland
| | - Roshan Krishna Kumar
- National
Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Department
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, United Kingdom
- ICFO-Institut
de Ciencies Fotoniques, The Barcelona Institute
of Science and Technology, Barcelona 08028, Spain
| | - Aitor Garcia-Ruiz
- National
Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Department
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, United Kingdom
| | - Giulia Zheng
- Laboratory
for Solid State Physics, ETH Zürich, Zürich CH-8093, Switzerland
| | - Elías Portolés
- Laboratory
for Solid State Physics, ETH Zürich, Zürich CH-8093, Switzerland
| | | | - Andre K. Geim
- National
Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Department
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, United Kingdom
| | - Kenji Watanabe
- National
Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National
Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Vladimir Fal’ko
- National
Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
- Department
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, United Kingdom
- Henry
Royce
Institute for Advanced Materials, Manchester M13 9PL, United Kingdom
| | - Klaus Ensslin
- Laboratory
for Solid State Physics, ETH Zürich, Zürich CH-8093, Switzerland
| | - Thomas Ihn
- Laboratory
for Solid State Physics, ETH Zürich, Zürich CH-8093, Switzerland
| | - Peter Rickhaus
- Laboratory
for Solid State Physics, ETH Zürich, Zürich CH-8093, Switzerland
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5
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Rao Q, Kang WH, Xue H, Ye Z, Feng X, Watanabe K, Taniguchi T, Wang N, Liu MH, Ki DK. Ballistic transport spectroscopy of spin-orbit-coupled bands in monolayer graphene on WSe 2. Nat Commun 2023; 14:6124. [PMID: 37777513 PMCID: PMC10542375 DOI: 10.1038/s41467-023-41826-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 09/20/2023] [Indexed: 10/02/2023] Open
Abstract
Van der Waals interactions with transition metal dichalcogenides were shown to induce strong spin-orbit coupling (SOC) in graphene, offering great promises to combine large experimental flexibility of graphene with unique tuning capabilities of the SOC. Here, we probe SOC-driven band splitting and electron dynamics in graphene on WSe2 by measuring ballistic transverse magnetic focusing. We found a clear splitting in the first focusing peak whose evolution in charge density and magnetic field is well reproduced by calculations using the SOC strength of ~ 13 meV, and no splitting in the second peak that indicates stronger Rashba SOC. Possible suppression of electron-electron scatterings was found in temperature dependence measurement. Further, we found that Shubnikov-de Haas oscillations exhibit a weaker band splitting, suggesting that it probes different electron dynamics, calling for a new theory. Our study demonstrates an interesting possibility to exploit ballistic electron motion pronounced in graphene for emerging spin-orbitronics.
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Affiliation(s)
- Qing Rao
- Department of Physics and HK Institute of Quantum Science & Technology, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Wun-Hao Kang
- Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University, Tainan, 70101, Taiwan
| | - Hongxia Xue
- Department of Physics and HK Institute of Quantum Science & Technology, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Ziqing Ye
- Department of Physics and Center for Quantum Materials, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, 999077, Hong Kong, China
| | - Xuemeng Feng
- Department of Physics and Center for Quantum Materials, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, 999077, Hong Kong, China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Ning Wang
- Department of Physics and Center for Quantum Materials, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, 999077, Hong Kong, China
| | - Ming-Hao Liu
- Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University, Tainan, 70101, Taiwan.
| | - Dong-Keun Ki
- Department of Physics and HK Institute of Quantum Science & Technology, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
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6
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Vallejo Bustamante J, Ribeiro-Palau R, Fermon C, Pannetier-Lecoeur M, Watanabe K, Tanigushi T, Deblock R, Guéron S, Ferrier M, Fuchs JN, Montambaux G, Piéchon F, Bouchiat H. Paramagnetic Singularities of the Orbital Magnetism in Graphene with a Moiré Potential. PHYSICAL REVIEW LETTERS 2023; 131:116201. [PMID: 37774305 DOI: 10.1103/physrevlett.131.116201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 07/07/2023] [Indexed: 10/01/2023]
Abstract
The recent detection of the singular diamagnetism of Dirac electrons in a single graphene layer paved a new way of probing 2D quantum materials through the measurement of equilibrium orbital currents which cannot be accessed in usual transport experiments. Among the theoretical predictions is an intriguing orbital paramagnetism at saddle points of the dispersion relation. Here we present magnetization measurements in graphene monolayers aligned on hexagonal boron nitride crystals. Besides the sharp diamagnetic McClure response at the Dirac point, we detect extra diamagnetic singularities at the satellite Dirac points of the moiré lattice. Surrounding these diamagnetic satellite peaks, we also observe paramagnetic peaks located at the chemical potential of the saddle points of the graphene moiré band structure and relate them to the presence of van Hove logarithmic singularities in the density of states. These findings reveal the long ago predicted anomalous paramagnetic orbital response in 2D systems when the Fermi energy is tuned to the vicinity of saddle points.
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Affiliation(s)
- J Vallejo Bustamante
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | | | - C Fermon
- SPEC, CEA, CNRS, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
| | | | - K Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Tanigushi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - R Deblock
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - S Guéron
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - M Ferrier
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - J N Fuchs
- Sorbonne Université, CNRS, Laboratoire de Physique Théorique de la Matière Condensée, LPTMC, 75005 Paris, France
| | - G Montambaux
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - F Piéchon
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - H Bouchiat
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
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7
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Chen M, Zhong Y, Harris E, Li J, Zheng Z, Chen H, Wu JS, Jarillo-Herrero P, Ma Q, Edgar JH, Lin X, Dai S. Van der Waals isotope heterostructures for engineering phonon polariton dispersions. Nat Commun 2023; 14:4782. [PMID: 37553366 PMCID: PMC10409777 DOI: 10.1038/s41467-023-40449-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 07/26/2023] [Indexed: 08/10/2023] Open
Abstract
Element isotopes are characterized by distinct atomic masses and nuclear spins, which can significantly influence material properties. Notably, however, isotopes in natural materials are homogenously distributed in space. Here, we propose a method to configure material properties by repositioning isotopes in engineered van der Waals (vdW) isotopic heterostructures. We showcase the properties of hexagonal boron nitride (hBN) isotopic heterostructures in engineering confined photon-lattice waves-hyperbolic phonon polaritons. By varying the composition, stacking order, and thicknesses of h10BN and h11BN building blocks, hyperbolic phonon polaritons can be engineered into a variety of energy-momentum dispersions. These confined and tailored polaritons are promising for various nanophotonic and thermal functionalities. Due to the universality and importance of isotopes, our vdW isotope heterostructuring method can be applied to engineer the properties of a broad range of materials.
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Affiliation(s)
- M Chen
- Materials Research and Education Center, Department of Mechanical Engineering, Auburn University, Auburn, AL, 36849, USA
| | - Y Zhong
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, ZJU-Hangzhou Global Science and Technology Innovation Center, Zhejiang University, Hangzhou, 310027, China
| | - E Harris
- Department of Physics, Boston College, Chestnut Hill, Massachusetts, MA, 02467, USA
| | - J Li
- Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506, USA
| | - Z Zheng
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, MA, 02139, USA
| | - H Chen
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, ZJU-Hangzhou Global Science and Technology Innovation Center, Zhejiang University, Hangzhou, 310027, China
- International Joint Innovation Center, The Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, 314400, China
| | - J-S Wu
- Department of Photonics and Institute of Electro-Optical Engineering, National Yang Ming Chiao Tung University, Hsinchu, 30050, Taiwan
| | - P Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, MA, 02139, USA
| | - Q Ma
- Department of Physics, Boston College, Chestnut Hill, Massachusetts, MA, 02467, USA
| | - J H Edgar
- Tim Taylor Department of Chemical Engineering, Kansas State University, Manhattan, KS, 66506, USA
| | - X Lin
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, ZJU-Hangzhou Global Science and Technology Innovation Center, Zhejiang University, Hangzhou, 310027, China
| | - S Dai
- Materials Research and Education Center, Department of Mechanical Engineering, Auburn University, Auburn, AL, 36849, USA.
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8
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Mullan C, Slizovskiy S, Yin J, Wang Z, Yang Q, Xu S, Yang Y, Piot BA, Hu S, Taniguchi T, Watanabe K, Novoselov KS, Geim AK, Fal'ko VI, Mishchenko A. Mixing of moiré-surface and bulk states in graphite. Nature 2023; 620:756-761. [PMID: 37468634 PMCID: PMC10447246 DOI: 10.1038/s41586-023-06264-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2022] [Accepted: 05/25/2023] [Indexed: 07/21/2023]
Abstract
Van der Waals assembly enables the design of electronic states in two-dimensional (2D) materials, often by superimposing a long-wavelength periodic potential on a crystal lattice using moiré superlattices1-9. This twistronics approach has resulted in numerous previously undescribed physics, including strong correlations and superconductivity in twisted bilayer graphene10-12, resonant excitons, charge ordering and Wigner crystallization in transition-metal chalcogenide moiré structures13-18 and Hofstadter's butterfly spectra and Brown-Zak quantum oscillations in graphene superlattices19-22. Moreover, twistronics has been used to modify near-surface states at the interface between van der Waals crystals23,24. Here we show that electronic states in three-dimensional (3D) crystals such as graphite can be tuned by a superlattice potential occurring at the interface with another crystal-namely, crystallographically aligned hexagonal boron nitride. This alignment results in several Lifshitz transitions and Brown-Zak oscillations arising from near-surface states, whereas, in high magnetic fields, fractal states of Hofstadter's butterfly draw deep into the bulk of graphite. Our work shows a way in which 3D spectra can be controlled using the approach of 2D twistronics.
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Affiliation(s)
- Ciaran Mullan
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - Sergey Slizovskiy
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Jun Yin
- Department of Physics and Astronomy, University of Manchester, Manchester, UK.
- State Key Laboratory of Mechanics and Control for Aerospace Structures, Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, Institute for Frontier Science, Nanjing University of Aeronautics and Astronautics, Nanjing, China.
| | - Ziwei Wang
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
| | - Qian Yang
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Shuigang Xu
- National Graphene Institute, University of Manchester, Manchester, UK
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, Hangzhou, China
| | - Yaping Yang
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Benjamin A Piot
- Laboratoire National des Champs Magnétiques Intenses (LNCMI), CNRS Université Grenoble Alpes, Université Toulouse 3, INSA Toulouse, EMFL, Grenoble, France
| | - Sheng Hu
- National Graphene Institute, University of Manchester, Manchester, UK
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China
| | | | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | - Kostya S Novoselov
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
| | - A K Geim
- Department of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Vladimir I Fal'ko
- Department of Physics and Astronomy, University of Manchester, Manchester, UK.
- National Graphene Institute, University of Manchester, Manchester, UK.
- Henry Royce Institute for Advanced Materials, Manchester, UK.
| | - Artem Mishchenko
- Department of Physics and Astronomy, University of Manchester, Manchester, UK.
- National Graphene Institute, University of Manchester, Manchester, UK.
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9
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Ingla-Aynés J, Manesco ALR, Ghiasi TS, Volosheniuk S, Watanabe K, Taniguchi T, van der Zant HSJ. Specular Electron Focusing between Gate-Defined Quantum Point Contacts in Bilayer Graphene. NANO LETTERS 2023; 23:5453-5459. [PMID: 37289250 PMCID: PMC10311585 DOI: 10.1021/acs.nanolett.3c00499] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 06/02/2023] [Indexed: 06/09/2023]
Abstract
We report multiterminal measurements in a ballistic bilayer graphene (BLG) channel, where multiple spin- and valley-degenerate quantum point contacts (QPCs) are defined by electrostatic gating. By patterning QPCs of different shapes along different crystallographic directions, we study the effect of size quantization and trigonal warping on transverse electron focusing (TEF). Our TEF spectra show eight clear peaks with comparable amplitudes and weak signatures of quantum interference at the lowest temperature, indicating that reflections at the gate-defined edges are specular, and transport is phase coherent. The temperature dependence of the focusing signal shows that, despite the small gate-induced bandgaps in our sample (≲45 meV), several peaks are visible up to 100 K. The achievement of specular reflection, which is expected to preserve the pseudospin information of the electron jets, is promising for the realization of ballistic interconnects for new valleytronic devices.
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Affiliation(s)
- Josep Ingla-Aynés
- Kavli
Institute of Nanoscience, Delft University
of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - Antonio L. R. Manesco
- Kavli
Institute of Nanoscience, Delft University
of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - Talieh S. Ghiasi
- Kavli
Institute of Nanoscience, Delft University
of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - Serhii Volosheniuk
- Kavli
Institute of Nanoscience, Delft University
of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - 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
| | - Herre S. J. van der Zant
- Kavli
Institute of Nanoscience, Delft University
of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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10
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Kaplan D, Holder T, Yan B. General nonlinear Hall current in magnetic insulators beyond the quantum anomalous Hall effect. Nat Commun 2023; 14:3053. [PMID: 37236923 DOI: 10.1038/s41467-023-38734-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Accepted: 05/08/2023] [Indexed: 05/28/2023] Open
Abstract
Can a generic magnetic insulator exhibit a Hall current? The quantum anomalous Hall effect (QAHE) is one example of an insulating bulk carrying a quantized Hall conductivity while insulators with zero Chern number present zero Hall conductance in the linear response regime. Here, we find that a general magnetic insulator possesses a nonlinear Hall conductivity quadratic to the electric field if the system breaks inversion symmetry, which can be identified as a new type of multiferroic coupling. This conductivity originates from an induced orbital magnetization due to virtual interband transitions. We identify three contributions to the wavepacket motion, a velocity shift, a positional shift, and a Berry curvature renormalization. In contrast to the crystalline solid, we find that this nonlinear Hall conductivity vanishes for Landau levels of a 2D electron gas, indicating a fundamental difference between the QAHE and the integer quantum Hall effect.
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Affiliation(s)
- Daniel Kaplan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 7610001, Israel
| | - Tobias Holder
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 7610001, Israel
| | - Binghai Yan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 7610001, Israel.
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11
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Nathawat J, Mansaray I, Sakanashi K, Wada N, Randle MD, Yin S, He K, Arabchigavkani N, Dixit R, Barut B, Zhao M, Ramamoorthy H, Somphonsane R, Kim GH, Watanabe K, Taniguchi T, Aoki N, Han JE, Bird JP. Signatures of hot carriers and hot phonons in the re-entrant metallic and semiconducting states of Moiré-gapped graphene. Nat Commun 2023; 14:1507. [PMID: 36932096 PMCID: PMC10023744 DOI: 10.1038/s41467-023-37292-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Accepted: 03/09/2023] [Indexed: 03/19/2023] Open
Abstract
Stacking of graphene with hexagonal boron nitride (h-BN) can dramatically modify its bands from their usual linear form, opening a series of narrow minigaps that are separated by wider minibands. While the resulting spectrum offers strong potential for use in functional (opto)electronic devices, a proper understanding of the dynamics of hot carriers in these bands is a prerequisite for such applications. In this work, we therefore apply a strategy of rapid electrical pulsing to drive carriers in graphene/h-BN heterostructures deep into the dissipative limit of strong electron-phonon coupling. By using electrical gating to move the chemical potential through the "Moiré bands", we demonstrate a cyclical evolution between metallic and semiconducting states. This behavior is captured in a self-consistent model of non-equilibrium transport that considers the competition of electrically driven inter-band tunneling and hot-carrier scattering by strongly non-equilibrium phonons. Overall, our results demonstrate how a treatment of the dynamics of both hot carriers and hot phonons is essential to understanding the properties of functional graphene superlattices.
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Affiliation(s)
- Jubin Nathawat
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Ishiaka Mansaray
- Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Kohei Sakanashi
- Department of Materials Science, Chiba University, Inage-ku, Chiba, 263-8522, Japan
| | - Naoto Wada
- Department of Materials Science, Chiba University, Inage-ku, Chiba, 263-8522, Japan
| | - Michael D Randle
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Shenchu Yin
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Keke He
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Nargess Arabchigavkani
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Ripudaman Dixit
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Bilal Barut
- Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA
| | - Miao Zhao
- High-Frequency High-Voltage Device and Integrated Circuits Center, Institute of Microelectronics of Chinese Academy of Sciences, 3 Beitucheng West Road, Chaoyang District, Beijing, 100029, PR China
| | - Harihara Ramamoorthy
- Department of Electronics Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok, 10520, Thailand
| | - Ratchanok Somphonsane
- Department of Physics, Faculty of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok, 10520, Thailand
| | - Gil-Ho Kim
- School of Electronic and Electrical Engineering and Sungkyunkwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 16419, Korea
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, 305-0044, Japan
| | - Nobuyuki Aoki
- Department of Materials Science, Chiba University, Inage-ku, Chiba, 263-8522, Japan
| | - Jong E Han
- Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA.
| | - Jonathan P Bird
- Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA. .,Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY, 14260, USA.
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12
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Gupta S, Joshi P, Sachan R, Narayan J. Fabricating Graphene Oxide/h-BN Metal Insulator Semiconductor Diodes by Nanosecond Laser Irradiation. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:2718. [PMID: 35957151 PMCID: PMC9370297 DOI: 10.3390/nano12152718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 08/02/2022] [Accepted: 08/03/2022] [Indexed: 06/15/2023]
Abstract
To employ graphene's rapid conduction in 2D devices, a heterostructure with a broad bandgap dielectric that is free of traps is required. Within this paradigm, h-BN is a good candidate because of its graphene-like structure and ultrawide bandgap. We show how to make such a heterostructure by irradiating alternating layers of a-C and a-BN film with a nanosecond excimer laser, melting and zone-refining constituent layers in the process. With Raman spectroscopy and ToF-SIMS analyses, we demonstrate this localized zone-refining into phase-pure h-BN and rGO films with distinct Raman vibrational modes and SIMS profile flattening after laser irradiation. Furthermore, in comparing laser-irradiated rGO-Si MS and rGO/h-BN/Si MIS diodes, the MIS diodes exhibit an increased turn-on voltage (4.4 V) and low leakage current. The MIS diode I-V characteristics reveal direct tunneling conduction under low bias and Fowler-Nordheim tunneling in the high-voltage regime, turning the MIS diode ON with improved rectification and current flow. This study sheds light on the nonequilibrium approaches to engineering h-BN and graphene heterostructures for ultrathin field effect transistor device development.
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Affiliation(s)
- Siddharth Gupta
- Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695, USA
- Intel Corporation, Rolner Acres Campus 3, Hillsboro, OR 97124, USA
| | - Pratik Joshi
- Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695, USA
- Intel Corporation, Rolner Acres Campus 3, Hillsboro, OR 97124, USA
| | - Ritesh Sachan
- School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, USA
| | - Jagdish Narayan
- Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695, USA
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13
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Wang T, Jiang X, Wang J, Liu Z, Song J, Liu Y. One-dimensional quantum channel in bent honeycomb nanoribbons. Phys Chem Chem Phys 2022; 24:9316-9323. [PMID: 35389407 DOI: 10.1039/d2cp00468b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The directionality of steering charge carriers is of great importance for the application of two-dimensional (2D) materials. Using the generalized Bloch theorem coupled with the self-consistent charge density-functional tight-binding method, we theoretically propose an approach to construct a one-dimensional (1D) quantum channel in honeycomb nanoribbons (NR) via in-plane bending deformation. Bending-induced pseudo-magnetic fields lead to Landau quantization and localize the electronic states along both edges of bent NR. These localized states form robust 1D quantum channels, whose energies can be linearly modulated through the bending angle. Our findings give new inspiration for the realization of transverse magnetic focusing (TMF) under zero magnetic fields and pave the way for the design of 2D material-based nano-devices via strain-engineering.
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Affiliation(s)
- Tong Wang
- Department of Physics and Hebei Advanced Thin Film Laboratory, Hebei Normal University, Shijiazhuang 050024, Hebei, China.
| | - Xi Jiang
- Department of Physics and Hebei Advanced Thin Film Laboratory, Hebei Normal University, Shijiazhuang 050024, Hebei, China.
| | - Jing Wang
- Department of Physics and Hebei Advanced Thin Film Laboratory, Hebei Normal University, Shijiazhuang 050024, Hebei, China.
| | - Zhao Liu
- Department of Physics and Hebei Advanced Thin Film Laboratory, Hebei Normal University, Shijiazhuang 050024, Hebei, China. .,Beijing Computational Science Research Center, Beijing 100193, China
| | - Juntao Song
- Department of Physics and Hebei Advanced Thin Film Laboratory, Hebei Normal University, Shijiazhuang 050024, Hebei, China.
| | - Ying Liu
- Department of Physics and Hebei Advanced Thin Film Laboratory, Hebei Normal University, Shijiazhuang 050024, Hebei, China. .,National Key Laboratory for Materials Simulation and Design, Beijing 100083, China
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14
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Berdyugin AI, Xin N, Gao H, Slizovskiy S, Dong Z, Bhattacharjee S, Kumaravadivel P, Xu S, Ponomarenko LA, Holwill M, Bandurin DA, Kim M, Cao Y, Greenaway MT, Novoselov KS, Grigorieva IV, Watanabe K, Taniguchi T, Fal'ko VI, Levitov LS, Kumar RK, Geim AK. Out-of-equilibrium criticalities in graphene superlattices. Science 2022; 375:430-433. [PMID: 35084955 DOI: 10.1126/science.abi8627] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy, whereas the filled bands underneath contribute little to conduction. Here, we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics that resemble those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common to all graphene-based superlattices.
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Affiliation(s)
- Alexey I Berdyugin
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - Na Xin
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - Haoyang Gao
- Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Sergey Slizovskiy
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - Zhiyu Dong
- Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Shubhadeep Bhattacharjee
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - P Kumaravadivel
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - Shuigang Xu
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - L A Ponomarenko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,Department of Physics, University of Lancaster, Lancaster LA1 4YW, UK
| | - Matthew Holwill
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - D A Bandurin
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - Minsoo Kim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - Yang Cao
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - M T Greenaway
- Department of Physics, Loughborough University, Loughborough LE11 3TU, UK.,School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK
| | - K S Novoselov
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - I V Grigorieva
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - K Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - V I Fal'ko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.,Henry Royce Institute for Advanced Materials, Manchester M13 9PL, UK
| | - L S Levitov
- Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Roshan Krishna Kumar
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.,Institut de Ciencies Fotoniques (ICFO), Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
| | - A K Geim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.,National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
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15
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Zhang X, Wu T, Yu C, Lu R. Ultrafast Interlayer Charge Separation, Enhanced Visible-Light Absorption, and Tunable Overpotential in Twisted Graphitic Carbon Nitride Bilayers for Water Splitting. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2104695. [PMID: 34515388 DOI: 10.1002/adma.202104695] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 07/14/2021] [Indexed: 06/13/2023]
Abstract
Moiré pattern superlattice formed by 2D van der Waals layered structures have attracted great attention for diverse applications. In experiments, the enhancement of catalytic performance in twisted bilayer systems is reported while its mechanism remains unclear. From high-accuracy first-principles and time-dependent ab initio nonadiabatic molecular dynamics calculations, ultrafast interlayer charge transfer within 120 fs, excellent charge separation, improved visible-light absorption, and satisfactory overpotentials for the hydrogen evolution and oxygen evolution reactions in twisted graphitic carbon nitride (g-C3 N4 ) bilayers are found, which are beneficial to photocatalytic, photo-electrocatalytic, or electrocatalytic water splitting. This work provides insightful guidance to advanced nanocatalysis based on twisted layered materials.
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Affiliation(s)
- Xirui Zhang
- Institute of Ultrafast Optical Physics, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094, P. R. China
| | - Tong Wu
- Institute of Ultrafast Optical Physics, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094, P. R. China
| | - Chao Yu
- Institute of Ultrafast Optical Physics, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094, P. R. China
| | - Ruifeng Lu
- Institute of Ultrafast Optical Physics, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, 210094, P. R. China
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16
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Zhou H, Xie T, Taniguchi T, Watanabe K, Young AF. Superconductivity in rhombohedral trilayer graphene. Nature 2021; 598:434-438. [PMID: 34469942 DOI: 10.1038/s41586-021-03926-0] [Citation(s) in RCA: 67] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 08/18/2021] [Indexed: 02/08/2023]
Abstract
To access superconductivity via the electric field effect in a clean, two-dimensional device is a central goal of nanoelectronics. Recently, superconductivity has been realized in graphene moiré heterostructures1-4; however, many of these structures are not mechanically stable, and experiments show signatures of strong disorder. Here we report the observation of superconductivity-manifesting as low or vanishing resistivity at sub-kelvin temperatures-in crystalline rhombohedral trilayer graphene5,6, a structurally metastable carbon allotrope. Superconductivity occurs in two distinct gate-tuned regions (SC1 and SC2), and is deep in the clean limit defined by the ratio of mean free path and superconducting coherence length. Mapping of the normal state Fermi surfaces by quantum oscillations reveals that both superconductors emerge from an annular Fermi sea, and are proximal to an isospin-symmetry-breaking transition where the Fermi surface degeneracy changes7. SC1 emerges from a paramagnetic normal state, whereas SC2 emerges from a spin-polarized, valley-unpolarized half-metal17 and violates the Pauli limit for in-plane magnetic fields by at least one order of magnitude8,9. We discuss our results in view of several mechanisms, including conventional phonon-mediated pairing10,11, pairing due to fluctuations of the proximal isospin order12, and intrinsic instabilities of the annular Fermi liquid13,14. Our observation of superconductivity in a clean and structurally simple two-dimensional metal provides a model system to test competing theoretical models of superconductivity without the complication of modelling disorder, while enabling new classes of field-effect controlled electronic devices based on correlated electron phenomena and ballistic electron transport.
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Affiliation(s)
- Haoxin Zhou
- Department of Physics, University of California, Santa Barbara, CA, USA
| | - Tian Xie
- Department of Physics, University of California, Santa Barbara, 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
| | - Andrea F Young
- Department of Physics, University of California, Santa Barbara, CA, USA.
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17
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Precision measurement of electron-electron scattering in GaAs/AlGaAs using transverse magnetic focusing. Nat Commun 2021; 12:5048. [PMID: 34413308 PMCID: PMC8376939 DOI: 10.1038/s41467-021-25327-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 08/04/2021] [Indexed: 11/23/2022] Open
Abstract
Electron-electron (e-e) interactions assume a cardinal role in solid-state physics. Quantifying the e-e scattering length is hence critical. In this paper we show that the mesoscopic phenomenon of transverse magnetic focusing (TMF) in two-dimensional electron systems forms a precise and sensitive technique to measure this length scale. Conversely we quantitatively demonstrate that e-e scattering is the predominant effect limiting TMF amplitudes in high-mobility materials. Using high-resolution kinetic simulations, we show that the TMF amplitude at a maximum decays exponentially as a function of the e-e scattering length, which leads to a ready approach to extract this length from the measured TMF amplitudes. The approach is applied to measure the temperature-dependent e-e scattering length in high-mobility GaAs/AlGaAs heterostructures. The simulations further reveal current vortices that accompany the cyclotron orbits - a collective phenomenon counterintuitive to the ballistic transport underlying a TMF setting. Electron-electron scattering plays a crucial role in many solid state phenomena; however, the direct measurement of electron-electron scattering length is challenging. Here, the authors use transverse magnetic focusing to measure this quantity in high-mobility GaAs/AlGaAs heterostructures.
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18
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Liu Y, Zeng C, Yu J, Zhong J, Li B, Zhang Z, Liu Z, Wang ZM, Pan A, Duan X. Moiré superlattices and related moiré excitons in twisted van der Waals heterostructures. Chem Soc Rev 2021; 50:6401-6422. [PMID: 33942837 DOI: 10.1039/d0cs01002b] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Recent advances in moiré superlattices and moiré excitons, such as quantum emission arrays, low-energy flat bands, and Mott insulators, have rapidly attracted attention in the fields of optoelectronics, materials, and energy research. The interlayer twist turns into a degree of freedom that alters the properties of the systems of materials, and the realization of moiré excitons also offers the feasibility of making artificial exciton crystals. Moreover, moiré excitons exhibit many exciting properties under the regulation of various external conditions, including spatial polarisation, alternating dipolar to alternating dipolar moments and gate-dependence to gate voltage dependence; all are pertinent to their applications in nano-photonics and quantum information. But the lag in theoretical development and the low-efficiency of processing technologies significantly limit the potential of moiré superlattice applications. In this review, we systematically summarise and discuss the recent progress in moiré superlattices and moiré excitons, and analyze the current challenges, and put forward relevant recommendations. There is no doubt that further research will lead to breakthroughs in their application and promote reforms and innovations in traditional solid-state physics and materials science.
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Affiliation(s)
- Yanping Liu
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China.
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19
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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.
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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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20
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Kraft R, Liu MH, Selvasundaram PB, Chen SC, Krupke R, Richter K, Danneau R. Anomalous Cyclotron Motion in Graphene Superlattice Cavities. PHYSICAL REVIEW LETTERS 2020; 125:217701. [PMID: 33275010 DOI: 10.1103/physrevlett.125.217701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 10/20/2020] [Indexed: 06/12/2023]
Abstract
We consider graphene superlattice miniband fermions probed by electronic interferometry in magnetotransport experiments. By decoding the observed Fabry-Pérot interference patterns together with our corresponding quantum transport simulations, we find that the Dirac quasiparticles originating from the superlattice minibands do not undergo conventional cyclotron motion but follow more subtle trajectories. In particular, dynamics at low magnetic fields is characterized by peculiar, straight trajectory segments. Our results provide new insights into superlattice miniband fermions and open up novel possibilities to use periodic potentials in electron optics experiments.
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Affiliation(s)
- Rainer Kraft
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe D-76021, Germany
- Institute of Physics, Karlsruhe Institute of Technology, Karlsruhe D-76049, Germany
| | - Ming-Hao Liu
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
| | - Pranauv Balaji Selvasundaram
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe D-76021, Germany
- Department of Materials and Earth Sciences, Technical University Darmstadt, Darmstadt D-64287, Germany
| | - Szu-Chao Chen
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
| | - Ralph Krupke
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe D-76021, Germany
- Department of Materials and Earth Sciences, Technical University Darmstadt, Darmstadt D-64287, Germany
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, Karlsruhe D-76021, Germany
| | - Klaus Richter
- Institut für Theoretische Physik, Universität Regensburg, Regensburg D-93040, Germany
| | - Romain Danneau
- Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe D-76021, Germany
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, Karlsruhe D-76021, Germany
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21
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LaGasse SW, Cress CD. Unveiling Electron Optics in Two-Dimensional Materials by Nonlocal Resistance Mapping. NANO LETTERS 2020; 20:6623-6629. [PMID: 32787176 DOI: 10.1021/acs.nanolett.0c02443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We propose a technique based on nonlocal resistance measurements for mapping transport in electron optics experiments. Utilizing tight-binding transport methods, we show how to use a four-terminal measurement to isolate the ballistic transport from a single lead of interest and reconstruct its contribution to the local density of states. This enables us to propose an experimentally tractable four-terminal device with via contacts for measuring Veselago lensing in a graphene p-n junction. Furthermore, we demonstrate how to extend this method as a scanning probe technique, implementing mapping of complex electron optics experiments including angled junctions, collimation optics, and beam steering. Our results highlight the fundamental importance of electron dephasing in ballistic transport and provide guidelines for isolating electron optics signals of interest. These findings unveil a fresh approach to performing electron optics experiments, with a plethora of two-dimensional material platforms to explore.
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Affiliation(s)
- Samuel W LaGasse
- NRC Postdoc Residing at the Electronics Science and Technology Division, United States Naval Research Laboratory, Washington D.C. D.C. 20375, United States
| | - Cory D Cress
- Electronics Science and Technology Division, United States Naval Research Laboratory, Washington D.C. 20375, United States
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22
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Enaldiev VV, Zólyomi V, Yelgel C, Magorrian SJ, Fal'ko VI. Stacking Domains and Dislocation Networks in Marginally Twisted Bilayers of Transition Metal Dichalcogenides. PHYSICAL REVIEW LETTERS 2020; 124:206101. [PMID: 32501062 DOI: 10.1103/physrevlett.124.206101] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 04/13/2020] [Indexed: 05/27/2023]
Abstract
We apply a multiscale modeling approach to study lattice reconstruction in marginally twisted bilayers of transition metal dichalcogenides (TMD). For this, we develop density functional theory parametrized interpolation formulae for interlayer adhesion energies of MoSe_{2}, WSe_{2}, MoS_{2}, and WS_{2}, combine those with elasticity theory, and analyze the bilayer lattice relaxation into mesoscale domain structures. Paying particular attention to the inversion asymmetry of TMD monolayers, we show that 3R and 2H stacking domains, separated by a network of dislocations develop for twist angles θ^{∘}<θ_{P}^{∘}∼2.5° and θ^{∘}<θ_{AP}^{∘}∼1° for, respectively, bilayers with parallel (P) and antiparallel (AP) orientation of the monolayer unit cells and suggest how the domain structures would manifest itself in local probe scanning of marginally twisted P and AP bilayers.
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Affiliation(s)
- V V Enaldiev
- National Graphene Institute, University of Manchester, Booth St. E. Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- Kotel'nikov Institute of Radio-engineering and Electronics of the Russian Academy of Sciences, 11-7 Mokhovaya St, Moscow 125009, Russia
| | - V Zólyomi
- National Graphene Institute, University of Manchester, Booth St. E. Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- Hartree Centre, STFC Daresbury Laboratory, Daresbury WA4 4AD, United Kingdom
| | - C Yelgel
- National Graphene Institute, University of Manchester, Booth St. E. Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- Recep Tayyip Erdogan University, Department of Electricity and Energy, Rize 53100, Turkey
| | - S J Magorrian
- National Graphene Institute, University of Manchester, Booth St. E. Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - V I Fal'ko
- National Graphene Institute, University of Manchester, Booth St. E. Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- Henry Royce Institute for Advanced Materials, University of Manchester, Manchester M13 9PL, United Kingdom
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23
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Bultinck N, Chatterjee S, Zaletel MP. Mechanism for Anomalous Hall Ferromagnetism in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2020; 124:166601. [PMID: 32383960 DOI: 10.1103/physrevlett.124.166601] [Citation(s) in RCA: 76] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 04/01/2020] [Indexed: 06/11/2023]
Abstract
Motivated by the recent observation of an anomalous Hall effect in twisted bilayer graphene, we use a lowest Landau level model to understand the origin of the underlying symmetry-broken correlated state. This effective model is rooted in the occurrence of Chern bands which arise due to the coupling between the graphene device and its encapsulating substrate. Our model exhibits a phase transition from a spin-valley polarized insulator to a partial or fully valley unpolarized metal as the bandwidth is increased relative to the interaction strength, consistent with experimental observations. In sharp contrast to standard quantum Hall ferromagnetism, the Chern number structure of the flat bands precludes an instability to an intervalley coherent phase, but allows for an excitonic vortex lattice at large interaction anisotropy.
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Affiliation(s)
- Nick Bultinck
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - Shubhayu Chatterjee
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - Michael P Zaletel
- Department of Physics, University of California, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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24
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Cheng J, Zhong S, Wan W, Chen X, Chen A, Cheng Y. Novel Graphene/In 2O 3 Nanocubes Preparation and Selective Electrochemical Detection for L-Lysine of Camellia nitidissima Chi. MATERIALS 2020; 13:ma13081999. [PMID: 32344715 PMCID: PMC7215595 DOI: 10.3390/ma13081999] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 04/17/2020] [Accepted: 04/20/2020] [Indexed: 11/16/2022]
Abstract
In this work, novel graphene/In2O3 (GR/In2O3) nanocubes were prepared via one-pot solvothermal treatment, reduction reaction, and successive annealing technology at 600 °C step by step. Interestingly, In2O3 with featured cubic morphology was observed to grow on multi-layered graphene nanosheets, forming novel GR/In2O3 nanocubes. The resulting nanocomposites were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), etc. Further investigations demonstrated that a selective electrochemical sensor based on the prepared GR/In2O3 nanocubes can be achieved. By using the prepared GR/In2O3-based electrochemical sensor, the enantioselective and chem-selective performance, as well as the optimal conditions for L-Lysine detection in Camellia nitidissima Chi, were evaluated. The experimental results revealed that the GR/In2O3 nanocube-based electrochemical sensor showed good chiral recognition features for L-lysine in Camellia nitidissima Chi with a linear range of 0.23–30 μmol·L−1, together with selectivity and anti-interference properties for other different amino acids in Camellia nitidissima Chi.
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Affiliation(s)
- Jinsheng Cheng
- Henry-Fork School of Food Sciences, Shaoguan University, Shaoguan 512005, China; (W.W.); (X.C.)
- Correspondence:
| | - Sheng Zhong
- Shipai Branch, Dongguan Environmental Protection Bureau, Dongguan 523330, China;
| | - Weihong Wan
- Henry-Fork School of Food Sciences, Shaoguan University, Shaoguan 512005, China; (W.W.); (X.C.)
- Foshan Qionglu Health Tech. Ltd., Foshan 528000, China;
| | - Xiaoyuan Chen
- Henry-Fork School of Food Sciences, Shaoguan University, Shaoguan 512005, China; (W.W.); (X.C.)
| | - Ali Chen
- School of Pharmacy, Guangdong Pharmaceutical University, Guangzhou 510006, China;
| | - Ying Cheng
- Foshan Qionglu Health Tech. Ltd., Foshan 528000, China;
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25
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Wang L, Makk P, Zihlmann S, Baumgartner A, Indolese DI, Watanabe K, Taniguchi T, Schönenberger C. Mobility Enhancement in Graphene by in situ Reduction of Random Strain Fluctuations. PHYSICAL REVIEW LETTERS 2020; 124:157701. [PMID: 32357042 DOI: 10.1103/physrevlett.124.157701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 03/16/2020] [Indexed: 06/11/2023]
Abstract
Microscopic corrugations are ubiquitous in graphene even when placed on atomically flat substrates. These result in random local strain fluctuations limiting the carrier mobility of high quality hBN-supported graphene devices. We present transport measurements in hBN-encapsulated devices where such strain fluctuations can be in situ reduced by increasing the average uniaxial strain. When ∼0.2% of uniaxial strain is applied to the graphene, an enhancement of the carrier mobility by ∼35% is observed while the residual doping reduces by ∼39%. We demonstrate a strong correlation between the mobility and the residual doping, from which we conclude that random local strain fluctuations are the dominant source of disorder limiting the mobility in these devices. Our findings are also supported by Raman spectroscopy measurements.
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Affiliation(s)
- Lujun Wang
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Péter Makk
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Department of Physics, Budapest University of Technology and Economics and Nanoelectronics Momentum Research Group of the Hungarian Academy of Sciences, Budafoki ut 8, 1111 Budapest, Hungary
| | - Simon Zihlmann
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Andreas Baumgartner
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - David I Indolese
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Christian Schönenberger
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
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26
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He WY, Goldhaber-Gordon D, Law KT. Giant orbital magnetoelectric effect and current-induced magnetization switching in twisted bilayer graphene. Nat Commun 2020; 11:1650. [PMID: 32246024 PMCID: PMC7125167 DOI: 10.1038/s41467-020-15473-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Accepted: 03/13/2020] [Indexed: 11/19/2022] Open
Abstract
Recently, quantum anomalous Hall effect with spontaneous ferromagnetism was observed in twisted bilayer graphenes (TBG) near 3/4 filling. Importantly, it was observed that an extremely small current can switch the direction of the magnetization. This offers the prospect of realizing low energy dissipation magnetic memories. However, the mechanism of the current-driven magnetization switching is poorly understood as the charge currents in graphenes are generally believed to be non-magnetic. In this work, we demonstrate that in TBG, the twisting and substrate induced symmetry breaking allow an out of plane orbital magnetization to be generated by a charge current. Moreover, the large Berry curvatures of the flat bands give the Bloch electrons large orbital magnetic moments so that a small current can generate a large orbital magnetization. We further demonstrate how the charge current can switch the magnetization of the ferromagnetic TBG near 3/4 filling as observed in the experiments. The mechanism of current-driven magnetization switching in twisted bilayer graphene (TBG) is poorly understood. Here, He et al. show that a small current can generate a large orbital magnetization due to symmetry breaking by the twisting and substrate in TBG, leading to a giant orbital magnetoelectric effect.
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Affiliation(s)
- Wen-Yu He
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
| | - David Goldhaber-Gordon
- Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA, 94305, USA.,Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA
| | - K T Law
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
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27
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Berdyugin AI, Tsim B, Kumaravadivel P, Xu SG, Ceferino A, Knothe A, Kumar RK, Taniguchi T, Watanabe K, Geim AK, Grigorieva IV, Fal’ko VI. Minibands in twisted bilayer graphene probed by magnetic focusing. SCIENCE ADVANCES 2020; 6:eaay7838. [PMID: 32494602 PMCID: PMC7164947 DOI: 10.1126/sciadv.aay7838] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 01/22/2020] [Indexed: 05/25/2023]
Abstract
Magnetic fields force ballistic electrons injected from a narrow contact to move along skipping orbits and form caustics. This leads to pronounced resistance peaks at nearby voltage probes as electrons are effectively focused inside them, a phenomenon known as magnetic focusing. This can be used not only for the demonstration of ballistic transport but also to study the electronic structure of metals. Here, we use magnetic focusing to probe narrowbands in graphene bilayers twisted at ~2°. Their minibands are found to support long-range ballistic transport limited at low temperatures by intrinsic electron-electron scattering. A voltage bias between the layers causes strong minivalley splitting and allows selective focusing for different minivalleys, which is of interest for using this degree of freedom in frequently discussed valleytronics.
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Affiliation(s)
- A. I. Berdyugin
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - B. Tsim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - P. Kumaravadivel
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - S. G. Xu
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - A. Ceferino
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - A. Knothe
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - R. Krishna Kumar
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - T. Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - K. Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - A. K. Geim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - I. V. Grigorieva
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Manchester M13 9PL, UK
| | - V. I. Fal’ko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Manchester M13 9PL, UK
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28
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Yao W, Fan L. Research on the correlation of mechanical properties of BN-graphene-BN/BN vertically-stacked nanostructures in the presence of interlayer sp 3 bonds and nanopores with temperature. Phys Chem Chem Phys 2020; 22:5920-5928. [PMID: 32109269 DOI: 10.1039/d0cp00179a] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this study, we investigate the coupling of an internal field (defect field-sp3 bonds and nanopores) and an external field (strain and temperature). Simultaneously, we provide a design idea of hybrid materials. The mechanical properties of hybrid materials under the condition of internal and external field coupling were studied. When nanopores and sp3 bonds are considered simultaneously, we found that internal (sp3 bonds and defects) and external field (temperature and strain fields) have a negative chain reaction on the mechanical properties of BN-graphene-BN/BN vertically-stacked nanostructures, and the negative chain reaction will gradually increase with the change in parameters (such as the increase in temperature). The sp3 bonds can be regarded as a special defect, which will increase the initial strain of the system. In addition, the mechanical properties of the nanostructure, containing square nanopores in the boron nitride region are most sensitive to temperature change, relative to the nanopore in the other two regions. Atoms (around square nanopores) are more likely to overcome the binding energy and lose stability from the inherent equilibrium position, relative to that of circular nanopores.
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Affiliation(s)
- Wenjuan Yao
- Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai, 200072, China.
| | - Lei Fan
- Department of Civil Engineering, Shanghai University, Shanghai, 200072, China.
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29
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Wang S, Zhao M, Zhang C, Yang S, Wang Y, Watanabe K, Taniguchi T, Hone J, Zhang X. Electron-hole hybridization in bilayer graphene. Natl Sci Rev 2020; 7:248-253. [PMID: 34692039 PMCID: PMC8288876 DOI: 10.1093/nsr/nwz212] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 12/05/2019] [Accepted: 12/05/2019] [Indexed: 11/30/2022] Open
Abstract
Band structure determines the motion of electrons in a solid, giving rise to exotic phenomena when properly engineered. Drawing an analogy between electrons and photons, artificially designed optical lattices indicate the possibility of a similar band modulation effect in graphene systems. Yet due to the fermionic nature of electrons, modulated electronic systems promise far richer categories of behaviors than those found in optical lattices. Here, we uncovered a strong modulation of electronic states in bilayer graphene subject to periodic potentials. We observed for the first time the hybridization of electron and hole sub-bands, resulting in local band gaps at both primary and secondary charge neutrality points. Such hybridization leads to the formation of flat bands, enabling the study of correlated effects in graphene systems. This work may provide a novel way to manipulate electronic states in layered systems, which is important to both fundamental research and application.
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Affiliation(s)
- Siqi Wang
- NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley, CA 94720, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Mervin Zhao
- NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley, CA 94720, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Changjian Zhang
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Sui Yang
- NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley, CA 94720, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Yuan Wang
- NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley, CA 94720, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Xiang Zhang
- NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley, CA 94720, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.,Faculties of Sciences and Engineering, University of Hong Kong, Hong Kong, China
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30
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Villegas-Lelovsky L, Paupitz R. Graphenylene-based nanoribbons for novel molecular electronic devices. Phys Chem Chem Phys 2020; 22:28365-28375. [PMID: 33300921 DOI: 10.1039/d0cp04188b] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In the last decade, graphene has been frequently cited as one of the most promising materials for nanoelectronics. However, despite its outstanding mechanical and electronic properties, its use in the production of real nanoelectronic devices usually imposes some practical difficulties. This happens mainly due to the fact that, in its pristine form, graphene is a gapless material. We investigate theoretically the possibility of obtaining rectifying nanodevices using another carbon based two dimensional material, namely the graphenylene. This material has the advantage of being an intrinsic semiconductor, posing as a promising material for nanoelectronics. By doping graphenylene, one could obtain 2-dimensional p-n junctions, which can be useful for the construction of low dimensional electronic devices. We propose 2-dimensional diodes in which a clear rectification effect was demonstrated, with a conducting threshold of approximately 1.5 eV in direct bias and current blocking with opposite bias. During these investigations were found specific configurations that could result in devices with Zener-like behavior. Also, one unexpected effect was identified, which was the existence of transmission dips in electronic conductance plots. This result is discussed as a related feature to what was found in graphene nanoribbon systems under external magnetic fields, even though the external field was not a necessary ingredient to obtain such effect in the present case.
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31
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Wang Z, Wang YB, Yin J, Tóvári E, Yang Y, Lin L, Holwill M, Birkbeck J, Perello DJ, Xu S, Zultak J, Gorbachev RV, Kretinin AV, Taniguchi T, Watanabe K, Morozov SV, Anđelković M, Milovanović SP, Covaci L, Peeters FM, Mishchenko A, Geim AK, Novoselov KS, Fal’ko VI, Knothe A, Woods CR. Composite super-moiré lattices in double-aligned graphene heterostructures. SCIENCE ADVANCES 2019; 5:eaay8897. [PMID: 32064323 PMCID: PMC6989342 DOI: 10.1126/sciadv.aay8897] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 10/22/2019] [Indexed: 05/30/2023]
Abstract
When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moiré pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moiré patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moiré pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moiré super cell.
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Affiliation(s)
- Zihao Wang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Yi Bo Wang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Yin
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
| | - E. Tóvári
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Y. Yang
- Department 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
| | - L. Lin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - M. Holwill
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Birkbeck
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - D. J. Perello
- Department 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
| | - Shuigang Xu
- Department 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
| | - J. Zultak
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - R. V. Gorbachev
- Department 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
- Henry Royce Institute for Advanced Materials, Oxford Road, Manchester M13 9PL, UK
| | - A. V. Kretinin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - T. Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - K. Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - S. V. Morozov
- Institute of Microelectronics Technology RAS, Chernogolovka 142432, Russia
| | - M. Anđelković
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - S. P. Milovanović
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - L. Covaci
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - F. M. Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - A. Mishchenko
- Department 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
| | - A. K. Geim
- Department 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
| | - K. S. Novoselov
- Department 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, Singapore 117546, Singapore
- Chongqing 2D Materials Institute, Liangjiang New Area, Chongqing 400714, China
| | - Vladimir I. Fal’ko
- Department 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
- Henry Royce Institute for Advanced Materials, Oxford Road, Manchester M13 9PL, UK
| | - Angelika Knothe
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - C. R. Woods
- Department 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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32
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Super-geometric electron focusing on the hexagonal Fermi surface of PdCoO 2. Nat Commun 2019; 10:5081. [PMID: 31705049 PMCID: PMC6841680 DOI: 10.1038/s41467-019-13020-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 10/11/2019] [Indexed: 11/08/2022] Open
Abstract
Geometric electron optics may be implemented in solids when electron transport is ballistic on the length scale of a device. Currently, this is realized mainly in 2D materials characterized by circular Fermi surfaces. Here we demonstrate that the nearly perfectly hexagonal Fermi surface of PdCoO2 gives rise to highly directional ballistic transport. We probe this directional ballistic regime in a single crystal of PdCoO2 by use of focused ion beam (FIB) micro-machining, defining crystalline ballistic circuits with features as small as 250 nm. The peculiar hexagonal Fermi surface naturally leads to enhanced electron self-focusing effects in a magnetic field compared to circular Fermi surfaces. This super-geometric focusing can be quantitatively predicted for arbitrary device geometry, based on the hexagonal cyclotron orbits appearing in this material. These results suggest a novel class of ballistic electronic devices exploiting the unique transport characteristics of strongly faceted Fermi surfaces. Ballistic electron beams in clean metals can be focused by passing currents through well designed contraptions, which is mostly done in isotropic materials described by a circular Fermi surface. Here, the authors demonstrate that the almost hexagonal Fermi surface of PdCoO2 gives rise to highly directional ballistic transport with enhanced electron self-focusing effects.
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33
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Bottom-up growth of homogeneous Moiré superlattices in bismuth oxychloride spiral nanosheets. Nat Commun 2019; 10:4472. [PMID: 31578330 PMCID: PMC6775108 DOI: 10.1038/s41467-019-12347-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 09/04/2019] [Indexed: 11/20/2022] Open
Abstract
Moiré superlattices (MSLs) are modulated structures produced from homogeneous or heterogeneous 2D layers stacked with a twist angle and/or lattice mismatch. Expanding the range of available materials, methods for fabricating MSL, and realization of unique emergent properties are key challenges. Here we report a facile bottom-up synthesis of homogeneous MSL based on a wide-gap 2D semiconductor, BiOCl, using a one-pot solvothermal approach with robust reproducibility. Unlike previous MSLs usually prepared by directly stacking two monolayers, our BiOCl MSLs are realized in a scalable, direct way through chemical growth of spiral-type nanosheets driven by screw-dislocations. We find emergent properties including large band gap reduction (∼0.6 eV), two-fold increase in carrier lifetime, and strongly enhanced photocatalytic activity. First-principles calculations reveal that such unusual properties can be ascribed to the locally enhanced inter-layer coupling associated with the Moiré potential modulation. Our results demonstrate the promise of MSL materials for chemical and physical functions. Expanding the range of available materials, methods for fabricating Moiré superlattices, and realization of new emergent properties are key challenges. Here the authors report a facile bottom-up synthesis of homogeneous Moiré superlattices based on a wide-gap 2D semiconductor, bismuth oxychloride.
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34
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Zheng X, Wang G, Huang F, Liu H, Gong C, Wen S, Hu Y, Zheng G, Chen D. Liquid Phase Exfoliated Hexagonal Boron Nitride/Graphene Heterostructure Based Electrode Toward Asymmetric Supercapacitor Application. Front Chem 2019; 7:544. [PMID: 31428602 PMCID: PMC6688068 DOI: 10.3389/fchem.2019.00544] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 07/16/2019] [Indexed: 11/14/2022] Open
Abstract
In this paper, owing to the electrostatic interaction between graphene and h-BN, a facile liquid phase exfoliation method was carried out to fabricate h-BN/graphene based van der Waals heterostructure nanocomposites without additional chemical cross-linkers. The physicochemical properties of as-prepared composites were characterized by several electron microscopic and spectroscopic measurements. The h-BN/graphene heterostructure composites were employed to use as the anodes of asymmetric supercapacitor, and exhibited exceptional capacitive performance due to their synergistic effects. It is expected that the as-prepared h-BN/graphene materials can boost scalable heterostructure electrodes in supercapacitors, and our liquid phase exfoliation method can be used for the construction of the other energy storage and electronics.
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Affiliation(s)
- Xuan Zheng
- Hubei Provincial Key Laboratory of Green Materials for Light Industry, School of Materials and Chemical Engineering, Hubei University of Technology, Wuhan, China
| | - Guangjin Wang
- School of Materials Science and Energy Engineering, Foshan University, Foshan, China.,College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan, China
| | - Fei Huang
- Key Laboratory of Functional Foods, Ministry of Agriculture, Guangdong Key Laboratory of Agricultural Products Processing, Sericultural & Agri-Food Research Institute Guangdong Academy of Agricultural Sciences, Guangzhou, China
| | - Hai Liu
- College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan, China
| | - Chunli Gong
- College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan, China
| | - Sheng Wen
- College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan, China
| | - Yuanqiang Hu
- College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan, China
| | - Genwen Zheng
- College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan, China
| | - Dongchu Chen
- School of Materials Science and Energy Engineering, Foshan University, Foshan, China
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35
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Cheng B, Pan C, Che S, Wang P, Wu Y, Watanabe K, Taniguchi T, Ge S, Lake R, Smirnov D, Lau CN, Bockrath M. Fractional and Symmetry-Broken Chern Insulators in Tunable Moiré Superlattices. NANO LETTERS 2019; 19:4321-4326. [PMID: 31204812 DOI: 10.1021/acs.nanolett.9b00811] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We study dual-gated graphene bilayer/hBN moiré superlattices. Under zero magnetic field, we observe additional resistance peaks as the charge density varies. The peaks' resistivities vary approximately quadratically with an applied perpendicular displacement field D. Data fit to a continuum model yield a bilayer/hBN interaction energy scale ∼30 ± 10 meV. Under a perpendicular magnetic field, we observe Hofstadter butterfly spectra as well as symmetry-broken and fractional Chern insulator states. Their topology and lattice symmetry breaking is D-tunable, enabling the realization of new topological states in this system.
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Affiliation(s)
- Bin Cheng
- Department of Physics and Astronomy , University of California , Riverside , California 92521 , United States
| | - Cheng Pan
- Department of Physics and Astronomy , University of California , Riverside , California 92521 , United States
| | - Shi Che
- Department of Physics and Astronomy , University of California , Riverside , California 92521 , United States
- Department of Physics , The Ohio State University , Columbus , Ohio 43221 , United States
| | - Peng Wang
- Department of Physics and Astronomy , University of California , Riverside , California 92521 , United States
| | - Yong Wu
- Department of Physics and Astronomy , University of California , Riverside , California 92521 , United States
| | - Kenji Watanabe
- National Institute for Materials Science , 1-1 Namiki Tsukuba , Ibaraki 305-0044 , Japan
| | - Takashi Taniguchi
- National Institute for Materials Science , 1-1 Namiki Tsukuba , Ibaraki 305-0044 , Japan
| | - Supeng Ge
- Department of Electrical and Computer Engineering , University of California , Riverside , California 92521 , United States
| | - Roger Lake
- Department of Electrical and Computer Engineering , University of California , Riverside , California 92521 , United States
| | - Dmitry Smirnov
- National High Magnetic Field Laboratory , Tallahassee , Florida 32310 , United States
| | - Chun Ning Lau
- Department of Physics , The Ohio State University , Columbus , Ohio 43221 , United States
| | - Marc Bockrath
- Department of Physics , The Ohio State University , Columbus , Ohio 43221 , United States
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36
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Wang L, Zihlmann S, Liu MH, Makk P, Watanabe K, Taniguchi T, Baumgartner A, Schönenberger C. New Generation of Moiré Superlattices in Doubly Aligned hBN/Graphene/hBN Heterostructures. NANO LETTERS 2019; 19:2371-2376. [PMID: 30803238 PMCID: PMC6463240 DOI: 10.1021/acs.nanolett.8b05061] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 02/21/2019] [Indexed: 05/27/2023]
Abstract
The specific rotational alignment of two-dimensional lattices results in a moiré superlattice with a larger period than the original lattices and allows one to engineer the electronic band structure of such materials. So far, transport signatures of such superlattices have been reported for graphene/hBN and graphene/graphene systems. Here we report moiré superlattices in fully hBN encapsulated graphene with both the top and the bottom hBN aligned to the graphene. In the graphene, two different moiré superlattices form with the top and the bottom hBN, respectively. The overlay of the two superlattices can result in a third superlattice with a period larger than the maximum period (14 nm) in the graphene/hBN system, which we explain in a simple model. This new type of band structure engineering allows one to artificially create an even wider spectrum of electronic properties in two-dimensional materials.
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Affiliation(s)
- Lujun Wang
- Department
of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University
of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Simon Zihlmann
- Department
of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Ming-Hao Liu
- Department
of Physics, National Cheng Kung University, Tainan 70101, Taiwan
| | - Péter Makk
- Department
of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Department
of Physics, Budapest University of Technology
and Economics and Nanoelectronics Momentum Research Group of the Hungarian
Academy of Sciences, Budafoki ut 8, 1111 Budapest, Hungary
| | - Kenji Watanabe
- National
Institute for Material Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- National
Institute for Material Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Andreas Baumgartner
- Department
of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University
of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Christian Schönenberger
- Department
of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University
of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
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37
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Jessen BS, Gammelgaard L, Thomsen MR, Mackenzie DMA, Thomsen JD, Caridad JM, Duegaard E, Watanabe K, Taniguchi T, Booth TJ, Pedersen TG, Jauho AP, Bøggild P. Lithographic band structure engineering of graphene. NATURE NANOTECHNOLOGY 2019; 14:340-346. [PMID: 30778216 DOI: 10.1038/s41565-019-0376-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 01/15/2019] [Indexed: 06/09/2023]
Abstract
Two-dimensional materials such as graphene allow direct access to the entirety of atoms constituting the crystal. While this makes shaping by lithography particularly attractive as a tool for band structure engineering through quantum confinement effects, edge disorder and contamination have so far limited progress towards experimental realization. Here, we define a superlattice in graphene encapsulated in hexagonal boron nitride, by etching an array of holes through the heterostructure with minimum feature sizes of 12-15 nm. We observe a magnetotransport regime that is distinctly different from the characteristic Landau fan of graphene, with a sizeable bandgap that can be tuned by a magnetic field. The measurements are accurately described by transport simulations and analytical calculations. Finally, we observe strong indications that the lithographically engineered band structure at the main Dirac point is cloned to a satellite peak that appears due to moiré interactions between the graphene and the encapsulating material.
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Affiliation(s)
- Bjarke S Jessen
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Lene Gammelgaard
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Morten R Thomsen
- Center for Nanostructured Graphene, Aalborg University, Aalborg, Denmark
- Department of Physics and Nanotechnology, Aalborg University, Aalborg, Denmark
| | - David M A Mackenzie
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- Department of Electronics and Nanoengineering, Aalto University, Aalto, Finland
| | - Joachim D Thomsen
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - José M Caridad
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Emil Duegaard
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - Timothy J Booth
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Thomas G Pedersen
- Center for Nanostructured Graphene, Aalborg University, Aalborg, Denmark
- Department of Physics and Nanotechnology, Aalborg University, Aalborg, Denmark
| | - Antti-Pekka Jauho
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene, Technical University of Denmark, Kongens Lyngby, Denmark.
- DTU Nanotech, Technical University of Denmark, Kgs. Lyngby, Denmark.
- DTU Physics, Technical University of Denmark, Kongens Lyngby, Denmark.
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38
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Jin C, Regan EC, Yan A, Iqbal Bakti Utama M, Wang D, Zhao S, Qin Y, Yang S, Zheng Z, Shi S, Watanabe K, Taniguchi T, Tongay S, Zettl A, Wang F. Observation of moiré excitons in WSe 2/WS 2 heterostructure superlattices. Nature 2019; 567:76-80. [PMID: 30804525 DOI: 10.1038/s41586-019-0976-y] [Citation(s) in RCA: 382] [Impact Index Per Article: 76.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Accepted: 01/17/2019] [Indexed: 11/09/2022]
Abstract
Moiré superlattices enable the generation of new quantum phenomena in two-dimensional heterostructures, in which the interactions between the atomically thin layers qualitatively change the electronic band structure of the superlattice. For example, mini-Dirac points, tunable Mott insulator states and the Hofstadter butterfly pattern can emerge in different types of graphene/boron nitride moiré superlattices, whereas correlated insulating states and superconductivity have been reported in twisted bilayer graphene moiré superlattices1-12. In addition to their pronounced effects on single-particle states, moiré superlattices have recently been predicted to host excited states such as moiré exciton bands13-15. Here we report the observation of moiré superlattice exciton states in tungsten diselenide/tungsten disulfide (WSe2/WS2) heterostructures in which the layers are closely aligned. These moiré exciton states manifest as multiple emergent peaks around the original WSe2 A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinct from that of the A exciton in WSe2 monolayers and in WSe2/WS2 heterostructures with large twist angles. These phenomena can be described by a theoretical model in which the periodic moiré potential is much stronger than the exciton kinetic energy and generates multiple flat exciton minibands. The moiré exciton bands provide an attractive platform from which to explore and control excited states of matter, such as topological excitons and a correlated exciton Hubbard model, in transition-metal dichalcogenides.
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Affiliation(s)
- Chenhao Jin
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - Emma C Regan
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, USA
| | - Aiming Yan
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - M Iqbal Bakti Utama
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, CA, USA
| | - Danqing Wang
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, USA
| | - Sihan Zhao
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - Ying Qin
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Sijie Yang
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Zhiren Zheng
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA
| | - Shenyang Shi
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Department of Physics, Fudan University, Shanghai, China
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - Sefaattin Tongay
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA
| | - Alex Zettl
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.,Kavli Energy NanoSciences Institute at University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Feng Wang
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA. .,Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. .,Kavli Energy NanoSciences Institute at University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
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39
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Rickhaus P, Wallbank J, Slizovskiy S, Pisoni R, Overweg H, Lee Y, Eich M, Liu MH, Watanabe K, Taniguchi T, Ihn T, Ensslin K. Transport Through a Network of Topological Channels in Twisted Bilayer Graphene. NANO LETTERS 2018; 18:6725-6730. [PMID: 30336041 DOI: 10.1021/acs.nanolett.8b02387] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We explore a network of electronic quantum valley Hall states in the moiré crystal of minimally twisted bilayer graphene. In our transport measurements, we observe Fabry-Pérot and Aharanov-Bohm oscillations that are robust in magnetic fields ranging from 0 to 8 T, which is in strong contrast to more conventional two-dimensional systems where trajectories in the bulk are bent by the Lorentz force. This persistence in magnetic field and the linear spacing in density indicate that charge carriers in the bulk flow in topologically protected, one-dimensional channels. With this work, we demonstrate coherent electronic transport in a lattice of topologically protected states.
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Affiliation(s)
- Peter Rickhaus
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
| | - John Wallbank
- Centre for Ecology and Hydrology , Maclean Building, Benson Lane , Crowmarsh Gifford, Wallingford, Oxfordshire , OX10 8BB , United Kingdom
| | | | - Riccardo Pisoni
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
| | - Hiske Overweg
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
| | - Yongjin Lee
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
| | - Marius Eich
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
| | - Ming-Hao Liu
- Department of Physics , National Cheng Kung University , Tainan 70101 , Taiwan
| | - Kenji Watanabe
- National Institute for Material Science , 1-1 Namiki , Tsukuba 305-0044 , Japan
| | - Takashi Taniguchi
- National Institute for Material Science , 1-1 Namiki , Tsukuba 305-0044 , Japan
| | - Thomas Ihn
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
| | - Klaus Ensslin
- Department of Physics , ETH Zürich , Otto-Stern-Weg 1 , 8093 Zürich , Switzerland
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40
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Indolese DI, Delagrange R, Makk P, Wallbank JR, Wanatabe K, Taniguchi T, Schönenberger C. Signatures of van Hove Singularities Probed by the Supercurrent in a Graphene-hBN Superlattice. PHYSICAL REVIEW LETTERS 2018; 121:137701. [PMID: 30312070 DOI: 10.1103/physrevlett.121.137701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Indexed: 06/08/2023]
Abstract
The band structure of graphene can be strongly modified if its lattice is aligned with the one of a boron nitride substrate. A moiré superlattice forms, which manifests itself by the appearance of new Dirac points, accompanied by van Hove singularities. In this work, we present supercurrent measurements in a Josephson junction made from such a graphene superlattice in the long and diffusive transport regime, where the critical current depends on the Thouless energy. We can then estimate the specific density of states of the graphene superlattice from the combined measurement of the critical current and the normal state resistance. The result matches with theoretical predictions and highlights the strong increase of the density of states at the van Hove singularities. By measuring the magnetic field dependence of the critical current, we find the presence of edge currents at these singularities. We explain it by the reduction of the Fermi velocity associated with the van Hove singularity, which suppresses the supercurrent in the bulk while the electrons at the edges remain less localized, resulting in an edge supercurrent. We attribute these different behaviors of the edges to defects or chemical doping.
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Affiliation(s)
- D I Indolese
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - R Delagrange
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - P Makk
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Department of Physics, Budapest University of Technology and Economics and Nanoelectronics Momentum Research Group of the Hungarian Academy of Sciences, Budafoki ut 8, 1111 Budapest, Hungary
| | - J R Wallbank
- National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
| | - K Wanatabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - C Schönenberger
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
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41
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Drienovsky M, Joachimsmeyer J, Sandner A, Liu MH, Taniguchi T, Watanabe K, Richter K, Weiss D, Eroms J. Commensurability Oscillations in One-Dimensional Graphene Superlattices. PHYSICAL REVIEW LETTERS 2018; 121:026806. [PMID: 30085762 DOI: 10.1103/physrevlett.121.026806] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Indexed: 06/08/2023]
Abstract
We report the experimental observation of commensurability oscillations (COs) in 1D graphene superlattices. The widely tunable periodic potential modulation in hBN-encapsulated graphene is generated via the interplay of nanopatterned few-layer graphene acting as a local bottom gate and a global Si back gate. The longitudinal magnetoresistance shows pronounced COs when the sample is tuned into the unipolar transport regime. We observe up to six CO minima, providing evidence for a long mean free path despite the potential modulation. Comparison to existing theories shows that small-angle scattering is dominant in hBN/graphene/hBN heterostructures. We observe robust COs persisting to temperatures exceeding T=150 K. At high temperatures, we find deviations from the predicted T dependence, which we ascribe to electron-electron scattering.
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Affiliation(s)
- Martin Drienovsky
- Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Jonas Joachimsmeyer
- Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Andreas Sandner
- Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Ming-Hao Liu
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
- Institute of Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - 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
| | - Klaus Richter
- Institute of Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Dieter Weiss
- Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Jonathan Eroms
- Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany
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42
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Forsythe C, Zhou X, Watanabe K, Taniguchi T, Pasupathy A, Moon P, Koshino M, Kim P, Dean CR. Band structure engineering of 2D materials using patterned dielectric superlattices. NATURE NANOTECHNOLOGY 2018; 13:566-571. [PMID: 29736033 DOI: 10.1038/s41565-018-0138-7] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 04/06/2018] [Indexed: 06/08/2023]
Abstract
The ability to manipulate electrons in two-dimensional materials with external electric fields provides a route to synthetic band engineering. By imposing artificially designed and spatially periodic superlattice potentials, electronic properties can be further altered beyond the constraints of naturally occurring atomic crystals1-5. Here, we report a new approach to fabricate high-mobility superlattice devices by integrating surface dielectric patterning with atomically thin van der Waals materials. By separating the device assembly and superlattice fabrication processes, we address the intractable trade-off between device processing and mobility degradation that constrains superlattice engineering in conventional systems. The improved electrostatics of atomically thin materials allows smaller wavelength superlattice patterns relative to previous demonstrations. Moreover, we observe the formation of replica Dirac cones in ballistic graphene devices with sub-40 nm wavelength superlattices and report fractal Hofstadter spectra6-8 under large magnetic fields from superlattices with designed lattice symmetries that differ from that of the host crystal. Our results establish a robust and versatile technique for band structure engineering of graphene and related van der Waals materials with dynamic tunability.
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Affiliation(s)
- Carlos Forsythe
- Department of Physics, Columbia University, New York, NY, USA
| | - Xiaodong Zhou
- Department of Physics, Columbia University, New York, NY, USA
- Laboratory of Advanced Materials, Fudan University, Shanghai, China
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | | | - Abhay Pasupathy
- Department of Physics, Columbia University, New York, NY, USA
| | - Pilkyung Moon
- NYU Shanghai, Shanghai, China
- NYU-ECNU Institute of Physics at NYU Shanghai, Shanghai, China
| | - Mikito Koshino
- Department of Physics, Osaka University, Toyonaka, Japan
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Cory R Dean
- Department of Physics, Columbia University, New York, NY, USA.
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43
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Esteve-Adell I, He J, Ramiro F, Atienzar P, Primo A, García H. Catalyst-free one step synthesis of large area vertically stacked N-doped graphene-boron nitride heterostructures from biomass source. NANOSCALE 2018; 10:4391-4397. [PMID: 29450410 DOI: 10.1039/c7nr08424b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A procedure for the one-step preparation of films of few-layer N-doped graphene on top of nanometric hexagonal boron nitride sheets ((N)graphene/h-BN) based on the pyrolysis at 900 °C under an inert atmosphere of a film of chitosan containing about 20 wt% of ammonium borate salt as a precursor is reported. During the pyrolysis a spontaneous segregation of (N)graphene and boron nitride layers takes place. The films were characterized by optical microscopy that shows a thin graphene overlayer covering the boron nitride layer, the latter showing characteristic cracks, and by XPS measurements at different monitoring angles from 0° to 50° where an increase in the proportion of C vs. B and N was observed. The resulting (N)graphene/h-BN films were also characterized by Raman, HRTEM, SEM, FIB-SEM and AFM. The thickness of the (N)graphene and h-BN layers can be controlled by varying the concentration of precursors and the spin coating rate and is typically below 5 nm. Electrical conductivity measurements using microelectrodes can cause the burning of the graphene layer at high intensities, while lower intensities show that (N)graphene/h-BN films behave as capacitors in the range of positive voltages.
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Affiliation(s)
- Ivan Esteve-Adell
- Instituto Universitario de Tecnología Química (CSIC-UPV), Universidad Politécnica de Valencia, Av. de los Naranjos s/n, 46022, Valencia, Spain.
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Spanton EM, Zibrov AA, Zhou H, Taniguchi T, Watanabe K, Zaletel MP, Young AF. Observation of fractional Chern insulators in a van der Waals heterostructure. Science 2018; 360:62-66. [PMID: 29496958 DOI: 10.1126/science.aan8458] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 02/13/2018] [Indexed: 01/24/2023]
Abstract
Topologically ordered phases are characterized by long-range quantum entanglement and fractional statistics rather than by symmetry breaking. First observed in a fractionally filled continuum Landau level, topological order has since been proposed to arise more generally at fractional fillings of topologically nontrivial Chern bands. Here we report the observation of gapped states at fractional fillings of Harper-Hofstadter bands arising from the interplay of a magnetic field and a superlattice potential in a bilayer graphene-hexagonal boron nitride heterostructure. We observed phases at fractional filling of bands with Chern indices [Formula: see text] Some of these phases, in [Formula: see text] and [Formula: see text] bands, are characterized by fractional Hall conductance-that is, they are known as fractional Chern insulators and constitute an example of topological order beyond Landau levels.
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Affiliation(s)
- Eric M Spanton
- California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
| | - Alexander A Zibrov
- Department of Physics, University of California, Santa Barbara, CA 93106, USA
| | - Haoxin Zhou
- Department of Physics, University of California, Santa Barbara, CA 93106, USA
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Michael P Zaletel
- Department of Physics, Princeton University, Princeton, NJ 08544, USA
| | - Andrea F Young
- Department of Physics, University of California, Santa Barbara, CA 93106, USA.
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Lucas A, Fong KC. Hydrodynamics of electrons in graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:053001. [PMID: 29251624 DOI: 10.1088/1361-648x/aaa274] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Generic interacting many-body quantum systems are believed to behave as classical fluids on long time and length scales. Due to rapid progress in growing exceptionally pure crystals, we are now able to experimentally observe this collective motion of electrons in solid-state systems, including graphene. We present a review of recent progress in understanding the hydrodynamic limit of electronic motion in graphene, written for physicists from diverse communities. We begin by discussing the 'phase diagram' of graphene, and the inevitable presence of impurities and phonons in experimental systems. We derive hydrodynamics, both from a phenomenological perspective and using kinetic theory. We then describe how hydrodynamic electron flow is visible in electronic transport measurements. Although we focus on graphene in this review, the broader framework naturally generalizes to other materials. We assume only basic knowledge of condensed matter physics, and no prior knowledge of hydrodynamics.
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Affiliation(s)
- Andrew Lucas
- Department of Physics, Stanford University, Stanford, CA 94305, United States of America
| | - Kin Chung Fong
- Raytheon BBN Technologies, Quantum Information Processing Group, Cambridge, MA 02138, United States of America
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Lin X, Lu JC, Shao Y, Zhang YY, Wu X, Pan JB, Gao L, Zhu SY, Qian K, Zhang YF, Bao DL, Li LF, Wang YQ, Liu ZL, Sun JT, Lei T, Liu C, Wang JO, Ibrahim K, Leonard DN, Zhou W, Guo HM, Wang YL, Du SX, Pantelides ST, Gao HJ. Intrinsically patterned two-dimensional materials for selective adsorption of molecules and nanoclusters. NATURE MATERIALS 2017; 16:717-721. [PMID: 28604716 DOI: 10.1038/nmat4915] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 05/03/2017] [Indexed: 06/07/2023]
Abstract
Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.
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Affiliation(s)
- X Lin
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - J C Lu
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - Y Shao
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - Y Y Zhang
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
- Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, USA
| | - X Wu
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - J B Pan
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - L Gao
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - S Y Zhu
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - K Qian
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - Y F Zhang
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - D L Bao
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - L F Li
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - Y Q Wang
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - Z L Liu
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - J T Sun
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - T Lei
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - C Liu
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - J O Wang
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - K Ibrahim
- Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
| | - D N Leonard
- Material Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37381, USA
| | - W Zhou
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
- Material Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37381, USA
| | - H M Guo
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - Y L Wang
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - S X Du
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
| | - S T Pantelides
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
- Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235, USA
| | - H-J Gao
- Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, China
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Abstract
The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.
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Tran S, Yang J, Gillgren N, Espiritu T, Shi Y, Watanabe K, Taniguchi T, Moon S, Baek H, Smirnov D, Bockrath M, Chen R, Lau CN. Surface transport and quantum Hall effect in ambipolar black phosphorus double quantum wells. SCIENCE ADVANCES 2017; 3:e1603179. [PMID: 28630916 PMCID: PMC5457033 DOI: 10.1126/sciadv.1603179] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 04/05/2017] [Indexed: 06/07/2023]
Abstract
Quantum wells (QWs) constitute one of the most important classes of devices in the study of two-dimensional (2D) systems. In a double-layer QW, the additional "which-layer" degree of freedom gives rise to celebrated phenomena, such as Coulomb drag, Hall drag, and exciton condensation. We demonstrate facile formation of wide QWs in few-layer black phosphorus devices that host double layers of charge carriers. In contrast to traditional QWs, each 2D layer is ambipolar and can be tuned into n-doped, p-doped, or intrinsic regimes. Fully spin-polarized quantum Hall states are observed on each layer, with an enhanced Landé g factor that is attributed to exchange interactions. Our work opens the door for using 2D semiconductors as ambipolar single, double, or wide QWs with unusual properties, such as high anisotropy.
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Affiliation(s)
- Son Tran
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- Department of Physics, Ohio State University, Columbus, OH 43220, USA
| | - Jiawei Yang
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- Department of Physics, Ohio State University, Columbus, OH 43220, USA
| | - Nathaniel Gillgren
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
| | - Timothy Espiritu
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
| | - Yanmeng Shi
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Seongphill Moon
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
| | - Hongwoo Baek
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
| | - Dmitry Smirnov
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
| | - Marc Bockrath
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- Department of Physics, Ohio State University, Columbus, OH 43220, USA
| | - Ruoyu Chen
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- Department of Physics, Ohio State University, Columbus, OH 43220, USA
| | - Chun Ning Lau
- Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
- Department of Physics, Ohio State University, Columbus, OH 43220, USA
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Absorptive pinhole collimators for ballistic Dirac fermions in graphene. Nat Commun 2017; 8:15418. [PMID: 28504264 PMCID: PMC5440660 DOI: 10.1038/ncomms15418] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 03/28/2017] [Indexed: 01/25/2023] Open
Abstract
Ballistic electrons in solids can have mean free paths far larger than the smallest features patterned by lithography. This has allowed development and study of solid-state electron-optical devices such as beam splitters and quantum point contacts, which have informed our understanding of electron flow and interactions. Recently, high-mobility graphene has emerged as an ideal two-dimensional semimetal that hosts unique chiral electron-optical effects due to its honeycomb crystalline lattice. However, this chiral transport prevents the simple use of electrostatic gates to define electron-optical devices in graphene. Here we present a method of creating highly collimated electron beams in graphene based on collinear pairs of slits, with absorptive sidewalls between the slits. By this method, we achieve beams with angular width 18° or narrower, and transmission matching classical ballistic predictions. Shaping and guiding the flow of ballistic electrons is at the core of electron optics; however in graphene this is hindered by chiral tunneling. Here, the authors experimentally demonstrate an electron collimator based on hBN-encapsulated ballistic graphene, capable of emitting narrow electron beams.
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