1
|
Hoke JC, Li Y, May-Mann J, Watanabe K, Taniguchi T, Bradlyn B, Hughes TL, Feldman BE. Uncovering the spin ordering in magic-angle graphene via edge state equilibration. Nat Commun 2024; 15:4321. [PMID: 38773076 PMCID: PMC11109299 DOI: 10.1038/s41467-024-48385-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 04/30/2024] [Indexed: 05/23/2024] Open
Abstract
The flat bands in magic-angle twisted bilayer graphene (MATBG) provide an especially rich arena to investigate interaction-driven ground states. While progress has been made in identifying the correlated insulators and their excitations at commensurate moiré filling factors, the spin-valley polarizations of the topological states that emerge at high magnetic field remain unknown. Here we introduce a technique based on twist-decoupled van der Waals layers that enables measurement of their electronic band structure and-by studying the backscattering between counter-propagating edge states-the determination of the relative spin polarization of their edge modes. We find that the symmetry-broken quantum Hall states that extend from the charge neutrality point in MATBG are spin unpolarized at even integer filling factors. The measurements also indicate that the correlated Chern insulator emerging from half filling of the flat valence band is spin unpolarized and suggest that its conduction band counterpart may be spin polarized.
Collapse
Affiliation(s)
- Jesse C Hoke
- Department of Physics, Stanford University, Stanford, CA, 94305, USA
- Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Yifan Li
- Department of Physics, Stanford University, Stanford, CA, 94305, USA
- Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Julian May-Mann
- Department of Physics, Stanford University, Stanford, CA, 94305, USA
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - 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
| | - Barry Bradlyn
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Taylor L Hughes
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Benjamin E Feldman
- Department of Physics, Stanford University, Stanford, CA, 94305, USA.
- Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA.
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
| |
Collapse
|
2
|
Munyan S, Rashidi A, Lygo AC, Kealhofer R, Stemmer S. Edge Channel Transmission through a Quantum Point Contact in the Two-Dimensional Topological Insulator Cadmium Arsenide. NANO LETTERS 2023. [PMID: 37307419 DOI: 10.1021/acs.nanolett.3c01263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Cadmium arsenide (Cd3As2) thin films feature a two-dimensional topological insulator (2D TI) phase for certain thicknesses, which theoretically hosts a set of counterpropagating helical edge statesA bar has been added to each symbol of the high-symmetry points of Cu(100) and Cu(111). The bar indicates the surface projected Brillouin zone. that are characteristic of a quantum spin Hall (QSH) insulator. In devices containing electrostatically defined junctions and for magnetic fields below a critical value, chiral edge modes of the quantum Hall effect can coexist with QSH-like edge modes. In this work, we use a quantum point contact (QPC) device to characterize edge modes in the 2D TI phase of Cd3As2 and to understand how they can be controllably transmitted, which is important for use in future quantum interference devices. We investigate equilibration among both types of modes and find non-spin-selective equilibration. We also demonstrate the effect of the magnetic field on suppressing equilibration. We discuss the potential role of QSH-like modes in a transmission pathway that precludes full pinch-off.
Collapse
Affiliation(s)
- Simon Munyan
- Materials Department, University of California, Santa Barbara, California 93106-5050, United States
| | - Arman Rashidi
- Materials Department, University of California, Santa Barbara, California 93106-5050, United States
| | - Alexander C Lygo
- Materials Department, University of California, Santa Barbara, California 93106-5050, United States
| | - Robert Kealhofer
- Materials Department, University of California, Santa Barbara, California 93106-5050, United States
| | - Susanne Stemmer
- Materials Department, University of California, Santa Barbara, California 93106-5050, United States
| |
Collapse
|
3
|
Yan J, Wu Y, Yuan S, Liu X, Pfeiffer LN, West KW, Liu Y, Fu H, Xie XC, Lin X. Anomalous quantized plateaus in two-dimensional electron gas with gate confinement. Nat Commun 2023; 14:1758. [PMID: 36997525 PMCID: PMC10064851 DOI: 10.1038/s41467-023-37495-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2022] [Accepted: 03/16/2023] [Indexed: 04/01/2023] Open
Abstract
AbstractQuantum information can be coded by the topologically protected edges of fractional quantum Hall (FQH) states. Investigation on FQH edges in the hope of searching and utilizing non-Abelian statistics has been a focused challenge for years. Manipulating the edges, e.g. to bring edges close to each other or to separate edges spatially, is a common and essential step for such studies. The FQH edge structures in a confined region are typically presupposed to be the same as that in the open region in analysis of experimental results, but whether they remain unchanged with extra confinement is obscure. In this work, we present a series of unexpected plateaus in a confined single-layer two-dimensional electron gas (2DEG), which are quantized at anomalous fractions such as 9/4, 17/11, 16/13 and the reported 3/2. We explain all the plateaus by assuming surprisingly larger filling factors in the confined region. Our findings enrich the understanding of edge states in the confined region and in the applications of gate manipulation, which is crucial for the experiments with quantum point contact and interferometer.
Collapse
|
4
|
Le Breton G, Delagrange R, Hong Y, Garg M, Watanabe K, Taniguchi T, Ribeiro-Palau R, Roulleau P, Roche P, Parmentier FD. Heat Equilibration of Integer and Fractional Quantum Hall Edge Modes in Graphene. PHYSICAL REVIEW LETTERS 2022; 129:116803. [PMID: 36154417 DOI: 10.1103/physrevlett.129.116803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Accepted: 08/01/2022] [Indexed: 06/16/2023]
Abstract
Hole-conjugate states of the fractional quantum Hall effect host counterpropagating edge channels which are thought to exchange charge and energy. These exchanges have been the subject of extensive theoretical and experimental works; in particular, it is yet unclear if the presence of integer quantum Hall edge channels stemming from fully filled Landau levels affects heat equilibration along the edge. In this Letter, we present heat transport measurements in quantum Hall states of graphene demonstrating that the integer channels can strongly equilibrate with the fractional ones, leading to markedly different regimes of quantized heat transport that depend on edge electrostatics. Our results allow for a better comprehension of the complex edge physics in the fractional quantum Hall regime.
Collapse
Affiliation(s)
- G Le Breton
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette cedex, France
| | - R Delagrange
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette cedex, France
| | - Y Hong
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies (C2N), 91120 Palaiseau, France
| | - M Garg
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette cedex, France
| | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, 305-0044 Tsukuba, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, 305-0044 Tsukuba, Japan
| | - R Ribeiro-Palau
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies (C2N), 91120 Palaiseau, France
| | - P Roulleau
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette cedex, France
| | - P Roche
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette cedex, France
| | - F D Parmentier
- Université Paris-Saclay, CEA, CNRS, SPEC, 91191 Gif-sur-Yvette cedex, France
| |
Collapse
|
5
|
Nicolí G, Adam C, Röösli MP, Märki P, Scharnetzky J, Reichl C, Wegscheider W, Ihn TM, Ensslin K. Spin-Selective Equilibration among Integer Quantum Hall Edge Channels. PHYSICAL REVIEW LETTERS 2022; 128:056802. [PMID: 35179909 DOI: 10.1103/physrevlett.128.056802] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 01/03/2022] [Accepted: 01/10/2022] [Indexed: 06/14/2023]
Abstract
The equilibration between quantum Hall edge modes is known to depend on the disorder potential and the steepness of the edge. Modern samples with higher mobilities and setups with lower electron temperatures call for a further exploration of the topic. We develop a framework to systematically measure and analyze the equilibration of many (up to 8) integer edge modes. Our results show that spin-selective coupling dominates even for non-neighboring channels with parallel spin. Changes in magnetic field and bulk density let us control the equilibration until it is almost completely suppressed and dominated only by individual microscopic scatterers. This method could serve as a guideline to investigate and design improved devices, and to study fractional and other exotic states.
Collapse
Affiliation(s)
- Giorgio Nicolí
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Christoph Adam
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Marc P Röösli
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Peter Märki
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Jan Scharnetzky
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Christian Reichl
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | | | - Thomas M Ihn
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| |
Collapse
|
6
|
Indolese DI, Karnatak P, Kononov A, Delagrange R, Haller R, Wang L, Makk P, Watanabe K, Taniguchi T, Schönenberger C. Compact SQUID Realized in a Double-Layer Graphene Heterostructure. NANO LETTERS 2020; 20:7129-7135. [PMID: 32872789 DOI: 10.1021/acs.nanolett.0c02412] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
2D systems that host 1D helical states are advantageous from the perspective of scalable topological quantum computation when coupled to a superconductor. Graphene is particularly promising for its high electronic quality, its versatility in van der Waals heterostructures, and its electron- and hole-like degenerate 0th Landau level. Here we study a compact double-layer graphene SQUID (superconducting quantum interference device), where the superconducting loop is reduced to the superconducting contacts connecting two parallel graphene Josephson junctions. Despite the small size of the SQUID, it is fully tunable by the independent gate control of the chemical potentials in both layers. Furthermore, both Josephson junctions show a skewed current-phase relationship, indicating the presence of superconducting modes with high transparency. In the quantum Hall regime, we measure a well-defined conductance plateau of 2e2/h indicative of counter-propagating edge channels in the two layers.
Collapse
Affiliation(s)
- David I Indolese
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Paritosh Karnatak
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Artem Kononov
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Raphaëlle Delagrange
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Roy Haller
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - 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, 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
- Research Center for Functional Materials, National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, 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
| |
Collapse
|
7
|
Liu CI, Scaletta DS, Patel DK, Kruskopf M, Levy A, Hill HM, Rigosi AF. Analysing quantized resistance behaviour in graphene Corbino p-n junction devices. JOURNAL OF PHYSICS D: APPLIED PHYSICS 2020; 53:10.1088/1361-6463/ab83bb. [PMID: 32831402 PMCID: PMC7431976 DOI: 10.1088/1361-6463/ab83bb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Just a few of the promising applications of graphene Corbino pnJ devices include two-dimensional Dirac fermion microscopes, custom programmable quantized resistors, and mesoscopic valley filters. In some cases, device scalability is crucial, as seen in fields like resistance metrology, where graphene devices are required to accommodate currents of the order 100 μA to be compatible with existing infrastructure. However, fabrication of these devices still poses many difficulties. In this work, unusual quantized resistances are observed in epitaxial graphene Corbino p-n junction devices held at the ν = 2 plateau (R H ≈ 12906 Ω) and agree with numerical simulations performed with the LTspice circuit simulator. The formulae describing experimental and simulated data are empirically derived for generalized placement of up to three current terminals and accurately reflects observed partial edge channel cancellation. These results support the use of ultraviolet lithography as a way to scale up graphene-based devices with suitably narrow junctions that could be applied in a variety of subfields.
Collapse
Affiliation(s)
- Chieh-I Liu
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, United States
| | - Dominick S Scaletta
- Department of Physics, Mount San Jacinto College, Menifee, CA 92584, United States
| | - Dinesh K Patel
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Mattias Kruskopf
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States
- Joint Quantum Institute, University of Maryland, College Park, MD 20742, United States
- Electricity Division, Physikalisch-Technische Bundesanstalt, Braunschweig 38116, Germany
| | - Antonio Levy
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States
| | - Heather M Hill
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States
| | - Albert F Rigosi
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, United States
| |
Collapse
|
8
|
Wang K, Harzheim A, Taniguchi T, Watanabei K, Lee JU, Kim P. Tunneling Spectroscopy of Quantum Hall States in Bilayer Graphene p-n Junctions. PHYSICAL REVIEW LETTERS 2019; 122:146801. [PMID: 31050489 DOI: 10.1103/physrevlett.122.146801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 01/08/2019] [Indexed: 06/09/2023]
Abstract
We report tunneling transport in spatially controlled networks of quantum Hall (QH) edge states in bilayer graphene. By manipulating the separation, location, and spatial span of QH edge states via gate-defined electrostatics, we observe resonant tunneling between copropagating QH states across incompressible strips. Employing spectroscopic tunneling measurements and an analytical model, we characterize the energy gap, width, density of states, and compressibility of the QH edge states with high precision and sensitivity within the same device. The capability to engineer the QH edge network also provides an opportunity to build future quantum electronic devices with electrostatic manipulation of QH edge states, supported by rich underlying physics.
Collapse
Affiliation(s)
- Ke Wang
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55116, USA
| | - Achim Harzheim
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Takashi Taniguchi
- National Institute for Materials Science, Namiki, Ibaraki 305-0044, Japan
| | - Kenji Watanabei
- National Institute for Materials Science, Namiki, Ibaraki 305-0044, Japan
| | - Ji Ung Lee
- College of Nanoscale Engineering and Technology Innovation, SUNY Polytechnic Institute, Albany, New York 12203, USA
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| |
Collapse
|
9
|
Ribeiro-Palau R, Chen S, Zeng Y, Watanabe K, Taniguchi T, Hone J, Dean CR. High-Quality Electrostatically Defined Hall Bars in Monolayer Graphene. NANO LETTERS 2019; 19:2583-2587. [PMID: 30839210 DOI: 10.1021/acs.nanolett.9b00351] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Realizing graphene's promise as an atomically thin and tunable platform for fundamental studies and future applications in quantum transport requires the ability to electrostatically define the geometry of the structure and control the carrier concentration, without compromising the quality of the system. Here, we demonstrate the working principle of a new generation of high-quality gate-defined graphene samples, where the challenge of doing so in a gapless semiconductor is overcome by using the ν = 0 insulating state, which emerges at modest applied magnetic fields. In order to verify that the quality of our devices is not compromised, we compare the electronic transport response of different sample geometries, paying close attention to fragile quantum states, such as the fractional quantum Hall states that are highly susceptible to disorder. The ability to define local depletion regions without compromising device quality establishes a new approach toward structuring graphene-based quantum transport devices.
Collapse
Affiliation(s)
- Rebeca Ribeiro-Palau
- Department of Physics , Columbia University , New York , New York 10027 , United States
- Department of Mechanical Engineering , Columbia University , New York , New York 10027 , United States
| | - Shaowen Chen
- Department of Physics , Columbia University , New York , New York 10027 , United States
- Department of Applied Physics and Applied Mathematics , Columbia University , New York , New York 10027 , United States
| | - Yihang Zeng
- Department of Physics , Columbia University , New York , New York 10027 , United States
| | - 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
| | - James Hone
- Department of Mechanical Engineering , Columbia University , New York , New York 10027 , United States
| | - Cory R Dean
- Department of Physics , Columbia University , New York , New York 10027 , United States
| |
Collapse
|
10
|
Banerjee A, Sundaresh A, Biswas S, Ganesan R, Sen D, Anil Kumar PS. Topological insulator n-p-n junctions in a magnetic field. NANOSCALE 2019; 11:5317-5324. [PMID: 30843549 DOI: 10.1039/c8nr10306b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Electrical transport in three dimensional topological insulators (TIs) occurs through spin-momentum locked topological surface states that enclose an insulating bulk. In the presence of a magnetic field, surface states get quantized into Landau levels giving rise to chiral edge states that are naturally spin-polarized due to spin momentum locking. It has been proposed that p-n junctions of TIs exposed to external magnetic fields can manifest unique spin dependent effects, apart from forming basic building blocks for highly functional spintronic devices. Here, for the first time we study electrostatically defined n-p-n junctions of dual-gated devices of the three dimensional topological insulator BiSbTe1.25Se1.75 in the presence of a strong magnetic field, revealing striking signatures of suppressed or enhanced electrical transport depending upon the chirality of quantum Hall edge states created at the n-p and p-n junction interfaces. Theoretical modeling combining the electrostatics of the dual gated TI n-p-n junction with the Landauer Buttiker formalism for transport through a network of chiral edge states explains our experimental data. Our work not only opens up a route towards exotic spintronic devices but also provides a test bed for investigating the unique signatures of quantum Hall effects in topological insulators.
Collapse
Affiliation(s)
- Abhishek Banerjee
- Department of Physics, Indian Institute of Science, Bengaluru 560012, India.
| | | | | | | | | | | |
Collapse
|
11
|
Wei DS, van der Sar T, Lee SH, Watanabe K, Taniguchi T, Halperin BI, Yacoby A. Electrical generation and detection of spin waves in a quantum Hall ferromagnet. Science 2018; 362:229-233. [PMID: 30309954 DOI: 10.1126/science.aar4061] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2017] [Accepted: 08/19/2018] [Indexed: 11/02/2022]
Abstract
Spin waves are collective excitations of magnetic systems. An attractive setting for studying long-lived spin-wave physics is the quantum Hall (QH) ferromagnet, which forms spontaneously in clean two-dimensional electron systems at low temperature and in a perpendicular magnetic field. We used out-of-equilibrium occupation of QH edge channels in graphene to excite and detect spin waves in magnetically ordered QH states. Our experiments provide direct evidence for long-distance spin-wave propagation through different ferromagnetic phases in the N = 0 Landau level, as well as across the insulating canted antiferromagnetic phase. Our results will enable experimental investigation of the fundamental magnetic properties of these exotic two-dimensional electron systems.
Collapse
Affiliation(s)
- Di S Wei
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | | | - Seung Hwan Lee
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | | | - Amir Yacoby
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA. .,Department of Physics, Harvard University, Cambridge, MA 02138, USA
| |
Collapse
|
12
|
Li J, Wen H, Watanabe K, Taniguchi T, Zhu J. Gate-Controlled Transmission of Quantum Hall Edge States in Bilayer Graphene. PHYSICAL REVIEW LETTERS 2018; 120:057701. [PMID: 29481178 DOI: 10.1103/physrevlett.120.057701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 12/01/2017] [Indexed: 06/08/2023]
Abstract
The edge states of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas carry key information of the bulk excitations. Here we demonstrate gate-controlled transmission of edge states in bilayer graphene through a potential barrier with tunable height. The backscattering rate is continuously varied from 0 to close to 1, with fractional quantized values corresponding to the sequential complete backscattering of individual modes. Our experiments demonstrate the feasibility to controllably manipulate edge states in bilayer graphene, thus opening the door to more complex experiments.
Collapse
Affiliation(s)
- Jing Li
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Hua Wen
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - 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
| | - Jun Zhu
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| |
Collapse
|
13
|
Hu J, Rigosi AF, Lee JU, Lee HY, Yang Y, Liu CI, Elmquist RE, Newell DB. Quantum transport in graphene p-n junctions with moiré superlattice modulation. PHYSICAL REVIEW. B 2018; 98:10.1103/PhysRevB.98.045412. [PMID: 30997442 PMCID: PMC6463535 DOI: 10.1103/physrevb.98.045412] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We present simulations of quantum transport in graphene p-n junctions (pnJs) in which moiré superlattice potentials are incorporated to demonstrate the interplay between pnJs and moiré superlattice potentials. It is shown that the longitudinal and Hall resistivity maps can be strongly modulated by the pnJ profile, junction height, and moiré potentials. Device resistance measurements are subsequently performed on graphene/hexagonal- boron-nitride heterostructure samples with accurate alignment of crystallographic orientations to complement and support the simulation results.
Collapse
Affiliation(s)
- Jiuning Hu
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
- Joint Quantum Institute, University of Maryland, College Park, Maryland 20742, USA
| | - Albert F. Rigosi
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
| | - Ji U. Lee
- College of Nanoscale Science and Engineering, State University of New York Polytechnic Institute, Albany, New York 12203, USA
| | - Hsin-Yen Lee
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
- Theiss Research, La Jolla, California 92037, USA
| | - Yanfei Yang
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
- Joint Quantum Institute, University of Maryland, College Park, Maryland 20742, USA
| | - Chieh-I Liu
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
- Graduate Institute of Applied Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Randolph E. Elmquist
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
| | - David B. Newell
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA
| |
Collapse
|
14
|
Calvo MR, de Juan F, Ilan R, Fox EJ, Bestwick AJ, Mühlbauer M, Wang J, Ames C, Leubner P, Brüne C, Zhang SC, Buhmann H, Molenkamp LW, Goldhaber-Gordon D. Interplay of Chiral and Helical States in a Quantum Spin Hall Insulator Lateral Junction. PHYSICAL REVIEW LETTERS 2017; 119:226401. [PMID: 29286805 DOI: 10.1103/physrevlett.119.226401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Indexed: 06/07/2023]
Abstract
We study the electronic transport across an electrostatically gated lateral junction in a HgTe quantum well, a canonical 2D topological insulator, with and without an applied magnetic field. We control the carrier density inside and outside a junction region independently and hence tune the number and nature of 1D edge modes propagating in each of those regions. Outside the bulk gap, the magnetic field drives the system to the quantum Hall regime, and chiral states propagate at the edge. In this regime, we observe fractional plateaus that reflect the equilibration between 1D chiral modes across the junction. As the carrier density approaches zero in the central region and at moderate fields, we observe oscillations in the resistance that we attribute to Fabry-Perot interference in the helical states, enabled by the broken time reversal symmetry. At higher fields, those oscillations disappear, in agreement with the expected absence of helical states when band inversion is lifted.
Collapse
Affiliation(s)
- M R Calvo
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- CIC nanoGUNE, 20018 Donostia-San Sebastian, Spain
- Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
| | - F de Juan
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - R Ilan
- Department of Physics, University of California, Berkeley, California 94720, USA
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
| | - E J Fox
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - A J Bestwick
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - M Mühlbauer
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - J Wang
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - C Ames
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - P Leubner
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - C Brüne
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - S C Zhang
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - H Buhmann
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - L W Molenkamp
- Physikalisches Institut (EP3) and Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - D Goldhaber-Gordon
- Department of Physics, Stanford University, Stanford, California 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| |
Collapse
|
15
|
Wei DS, van der Sar T, Sanchez-Yamagishi JD, Watanabe K, Taniguchi T, Jarillo-Herrero P, Halperin BI, Yacoby A. Mach-Zehnder interferometry using spin- and valley-polarized quantum Hall edge states in graphene. SCIENCE ADVANCES 2017; 3:e1700600. [PMID: 28835920 PMCID: PMC5562424 DOI: 10.1126/sciadv.1700600] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 07/14/2017] [Indexed: 05/31/2023]
Abstract
Confined to a two-dimensional plane, electrons in a strong magnetic field travel along the edge in one-dimensional quantum Hall channels that are protected against backscattering. These channels can be used as solid-state analogs of monochromatic beams of light, providing a unique platform for studying electron interference. Electron interferometry is regarded as one of the most promising routes for studying fractional and non-Abelian statistics and quantum entanglement via two-particle interference. However, creating an edge-channel interferometer in which electron-electron interactions play an important role requires a clean system and long phase coherence lengths. We realize electronic Mach-Zehnder interferometers with record visibilities of up to 98% using spin- and valley-polarized edge channels that copropagate along a pn junction in graphene. We find that interchannel scattering between same-spin edge channels along the physical graphene edge can be used to form beamsplitters, whereas the absence of interchannel scattering along gate-defined interfaces can be used to form isolated interferometer arms. Surprisingly, our interferometer is robust to dephasing effects at energies an order of magnitude larger than those observed in pioneering experiments on GaAs/AlGaAs quantum wells. Our results shed light on the nature of edge-channel equilibration and open up new possibilities for studying exotic electron statistics and quantum phenomena.
Collapse
Affiliation(s)
- Di S. Wei
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | | | - Javier D. Sanchez-Yamagishi
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Pablo Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | | | - Amir Yacoby
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| |
Collapse
|
16
|
Karalic M, Mittag C, Tschirky T, Wegscheider W, Ensslin K, Ihn T. Lateral p-n Junction in an Inverted InAs/GaSb Double Quantum Well. PHYSICAL REVIEW LETTERS 2017; 118:206801. [PMID: 28581788 DOI: 10.1103/physrevlett.118.206801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Indexed: 06/07/2023]
Abstract
We present transport measurements on a lateral p-n junction in an inverted InAs/GaSb double quantum well at zero and nonzero perpendicular magnetic fields. At a zero magnetic field, the junction exhibits diodelike behavior in accordance with the presence of a hybridization gap. With an increasing magnetic field, we explore the quantum Hall regime where spin-polarized edge states with the same chirality are either reflected or transmitted at the junction, whereas those of opposite chirality undergo a mixing process, leading to full equilibration along the width of the junction independent of spin. These results lay the foundations for using p-n junctions in InAs/GaSb double quantum wells to probe the transition between the topological quantum spin Hall and quantum Hall states.
Collapse
Affiliation(s)
- Matija Karalic
- Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland
| | | | - Thomas Tschirky
- Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland
| | | | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zurich, 8093 Zurich, Switzerland
| |
Collapse
|
17
|
Overweg H, Eggimann H, Liu MH, Varlet A, Eich M, Simonet P, Lee Y, Watanabe K, Taniguchi T, Richter K, Fal'ko VI, Ensslin K, Ihn T. Oscillating Magnetoresistance in Graphene p-n Junctions at Intermediate Magnetic Fields. NANO LETTERS 2017; 17:2852-2857. [PMID: 28383919 DOI: 10.1021/acs.nanolett.6b05318] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report on the observation of magnetoresistance oscillations in graphene p-n junctions. The oscillations have been observed for six samples, consisting of single-layer and bilayer graphene, and persist up to temperatures of 30 K, where standard Shubnikov-de Haas oscillations are no longer discernible. The oscillatory magnetoresistance can be reproduced by tight-binding simulations. We attribute this phenomenon to the modulated densities of states in the n- and p-regions.
Collapse
Affiliation(s)
- Hiske Overweg
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Hannah Eggimann
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Ming-Hao Liu
- Institut für Theoretische Physik, Universität Regensburg , D-93040 Regensburg, Germany
- Department of Physics, National Cheng Kung University , Tainan 70101, Taiwan
| | - Anastasia Varlet
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Marius Eich
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Pauline Simonet
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Yongjin Lee
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Material Science , 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Material Science , 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Klaus Richter
- Institut für Theoretische Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Vladimir I Fal'ko
- National Graphene Institute, University of Manchester , Manchester M13 9PL, United Kingdom
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich , CH-8093 Zürich, Switzerland
| |
Collapse
|
18
|
Tunable transmission of quantum Hall edge channels with full degeneracy lifting in split-gated graphene devices. Nat Commun 2017; 8:14983. [PMID: 28406152 PMCID: PMC5399284 DOI: 10.1038/ncomms14983] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 02/20/2017] [Indexed: 12/03/2022] Open
Abstract
Charge carriers in the quantum Hall regime propagate via one-dimensional conducting channels that form along the edges of a two-dimensional electron gas. Controlling their transmission through a gate-tunable constriction, also called quantum point contact, is fundamental for many coherent transport experiments. However, in graphene, tailoring a constriction with electrostatic gates remains challenging due to the formation of p–n junctions below gate electrodes along which electron and hole edge channels co-propagate and mix, short circuiting the constriction. Here we show that this electron–hole mixing is drastically reduced in high-mobility graphene van der Waals heterostructures thanks to the full degeneracy lifting of the Landau levels, enabling quantum point contact operation with full channel pinch-off. We demonstrate gate-tunable selective transmission of integer and fractional quantum Hall edge channels through the quantum point contact. This gate control of edge channels opens the door to quantum Hall interferometry and electron quantum optics experiments in the integer and fractional quantum Hall regimes of graphene. Quantum point contacts are gate-tunable constrictions allowing for control of charge carrier transmission in 2D electron gases. Here, the authors fabricate a hBN/graphene/hBN van der Waals heterojunction to enable quantum point contact devices in the integer and fractional quantum Hall regimes.
Collapse
|
19
|
Sanchez-Yamagishi JD, Luo JY, Young AF, Hunt BM, Watanabe K, Taniguchi T, Ashoori RC, Jarillo-Herrero P. Helical edge states and fractional quantum Hall effect in a graphene electron-hole bilayer. NATURE NANOTECHNOLOGY 2017; 12:118-122. [PMID: 27798608 DOI: 10.1038/nnano.2016.214] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 09/13/2016] [Indexed: 05/22/2023]
Abstract
Helical 1D electronic systems are a promising route towards realizing circuits of topological quantum states that exhibit non-Abelian statistics. Here, we demonstrate a versatile platform to realize 1D systems made by combining quantum Hall (QH) edge states of opposite chiralities in a graphene electron-hole bilayer at moderate magnetic fields. Using this approach, we engineer helical 1D edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong non-local transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Unlike other approaches used for realizing helical states, the graphene electron-hole bilayer can be used to build new 1D systems incorporating fractional edge states. Indeed, we are able to tune the bilayer devices into a regime hosting fractional and integer edge states of opposite chiralities, paving the way towards 1D helical conductors with fractional quantum statistics.
Collapse
Affiliation(s)
| | - Jason Y Luo
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Andrea F Young
- Department of Physics, University of California Santa Barbara, Santa Barbara, California 93106, USA
| | - Benjamin M Hunt
- Department of Physics, Carnegie Mellon University, Pittsburg, Pennsylvania 15213, USA
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Raymond C Ashoori
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Pablo Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| |
Collapse
|
20
|
Tóvári E, Makk P, Liu MH, Rickhaus P, Kovács-Krausz Z, Richter K, Schönenberger C, Csonka S. Gate-controlled conductance enhancement from quantum Hall channels along graphene p-n junctions. NANOSCALE 2016; 8:19910-19916. [PMID: 27878177 PMCID: PMC5315021 DOI: 10.1039/c6nr05100f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The formation of quantum Hall channels inside the bulk of graphene is studied using various contact and gate geometries. p-n junctions are created along the longitudinal direction of samples, and enhanced conductance is observed in the case of bipolar doping due to the new conducting channels formed in the bulk, whose position, propagating direction and, in one geometry, coupling to electrodes are determined by the gate-controlled filling factor across the device. This effect could be exploited to probe the behavior and interaction of quantum Hall channels protected against uncontrolled scattering at the edges.
Collapse
Affiliation(s)
- Endre Tóvári
- Department of Physics, Budapest University of Technology and Economics, and Condensed Matter Research Group of the Hungarian Academy of Sciences, Budafoki út 8, 1111 Budapest, Hungary.
| | - Péter Makk
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Ming-Hao Liu
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Peter Rickhaus
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Zoltán Kovács-Krausz
- Department of Physics, Budapest University of Technology and Economics, and Condensed Matter Research Group of the Hungarian Academy of Sciences, Budafoki út 8, 1111 Budapest, Hungary. and Faculty of Physics, Babes-Bolyai University, Str. Mihail Kogalniceanu nr. 1, 400084 Cluj-Napoca, Romania
| | - Klaus Richter
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Christian Schönenberger
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Szabolcs Csonka
- Department of Physics, Budapest University of Technology and Economics, and Condensed Matter Research Group of the Hungarian Academy of Sciences, Budafoki út 8, 1111 Budapest, Hungary.
| |
Collapse
|
21
|
Takei S, Yacoby A, Halperin BI, Tserkovnyak Y. Spin Superfluidity in the ν=0 Quantum Hall State of Graphene. PHYSICAL REVIEW LETTERS 2016; 116:216801. [PMID: 27284667 DOI: 10.1103/physrevlett.116.216801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Indexed: 06/06/2023]
Abstract
Strong electron interactions can lead to a variety of broken-symmetry phases in monolayer graphene. In the quantum Hall regime, the interaction effect are enhanced by the formation of highly degenerate Landau levels, catalyzing the emergence of such phases. Recent magnetotransport studies show evidence that the ν=0 quantum Hall state of graphene is in an insulating canted antiferromagnetic phase with the Néel vector lying within the graphene plane. Here, we show that this Néel order can be detected via two-terminal spin transport. We find that a dynamic and inhomogeneous texture of the Néel vector can mediate nearly dissipationless (superfluid) transport of spin angular momentum polarized along the z axis, which could serve as a strong support for the antiferromagnetic scenario. The injection and detection of spin current in the ν=0 region can be achieved using the two spin-polarized edge channels of the |ν|=2 quantum Hall state. Measurements of the dependence of the spin current on the length of the ν=0 region would provide direct evidence for spin superfluidity.
Collapse
Affiliation(s)
- So Takei
- Department of Physics, Queens College of the City University of New York, Queens, New York 11367, USA
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| | - Amir Yacoby
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Bertrand I Halperin
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Yaroslav Tserkovnyak
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
| |
Collapse
|
22
|
Zhao F, Xu L, Zhang J. Manipulating interface states in monolayer-bilayer graphene planar junctions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:185001. [PMID: 27050943 DOI: 10.1088/0953-8984/28/18/185001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report on transport properties of monolayer-bilayer graphene planar junctions in a magnetic field. Due to its unique geometry, the edge and interface states can be independently manipulated by either interlayer potential or Zeeman field, and the conductance exhibits interesting quantized behaviors. In the hybrid graphene junction, the quantum Hall (QH) conductance is no longer antisymmetric with respect to the charge neutrality point. When the Zeeman field is considered, a quantum spin Hall (QSH) phase is found in the monolayer region while the weak-QSH phase stays in the bilayer region. In the presence of both interlayer potential and Zeeman field, the bilayer region hosts a QSH phase, whereas the monolayer region is still in a QH phase, leading to a spin-polarized current in the interface. In particular, the QSH phase remains robust against the disorder.
Collapse
Affiliation(s)
- Fang Zhao
- School of Physics Science and Technology, Xinjiang University, Urumqi 830046, People's Republic of China
| | | | | |
Collapse
|
23
|
Matsuo S, Takeshita S, Tanaka T, Nakaharai S, Tsukagoshi K, Moriyama T, Ono T, Kobayashi K. Edge mixing dynamics in graphene p-n junctions in the quantum Hall regime. Nat Commun 2015; 6:8066. [PMID: 26337445 PMCID: PMC4569692 DOI: 10.1038/ncomms9066] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 07/13/2015] [Indexed: 11/09/2022] Open
Abstract
Massless Dirac electron systems such as graphene exhibit a distinct half-integer quantum Hall effect, and in the bipolar transport regime co-propagating edge states along the p–n junction are realized. Additionally, these edge states are uniformly mixed at the junction, which makes it a unique structure to partition electrons in these edge states. Although many experimental works have addressed this issue, the microscopic dynamics of electron partition in this peculiar structure remains unclear. Here we performed shot-noise measurements on the junction in the quantum Hall regime as well as at zero magnetic field. We found that, in sharp contrast with the zero-field case, the shot noise in the quantum Hall regime is finite in the bipolar regime, but is strongly suppressed in the unipolar regime. Our observation is consistent with the theoretical prediction and gives microscopic evidence that the edge states are uniquely mixed along the p–n junction. A graphene p–n junction can be created by connecting electrical gates that generate electron-doped and hole-doped areas in a flake. Here, the authors use shot-noise measurements to provide microscopic evidence that edge states are uniquely mixed along the junction in the quantum Hall regime.
Collapse
Affiliation(s)
- Sadashige Matsuo
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan.,Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Shunpei Takeshita
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Takahiro Tanaka
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | | | | | - Takahiro Moriyama
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Teruo Ono
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
| | - Kensuke Kobayashi
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
| |
Collapse
|
24
|
Kang H, Yun Y, Park J, Kim J, Truong TK, Kim JG, Park N, Yun H, Lee SW, Lee YH, Suh D. Quantum Hall conductance of graphene combined with charge-trap memory operation. NANOTECHNOLOGY 2015; 26:345202. [PMID: 26242388 DOI: 10.1088/0957-4484/26/34/345202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The combination of quantum Hall conductance and charge-trap memory operation was qualitatively examined using a graphene field-effect transistor. The characteristics of two terminal quantum Hall conductance appeared clearly on the background of a huge conductance hysteresis during a gate-voltage sweep for a device using monolayer graphene as a channel,hexagonal boron-nitride flakes as a tunneling dielectric and defective silicon oxide as the charge storage node. Even though there was a giant shift of the charge neutrality point, the deviation of quantized resistance value at the state of filling factor 2 was less than 1.6% from half of the von Klitzing constant. At high Landau level indices, the behaviors of quantum conductance oscillation between the increasing and the decreasing electron densities were identical in spite ofa huge memory window exceeding 100 V. Our results indicate that the two physical phenomena, two-terminal quantum Hall conductance and charge-trap memory operation, can be integrated into one device without affecting each other.
Collapse
|
25
|
Conductance oscillations induced by ballistic snake states in a graphene heterojunction. Nat Commun 2015; 6:6093. [PMID: 25652075 DOI: 10.1038/ncomms7093] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 12/11/2014] [Indexed: 11/08/2022] Open
Abstract
The realization of p-n junctions in graphene, combined with the gapless and chiral nature of its massless Dirac fermions has led to the observation of many intriguing phenomena such as the quantum Hall effect in the bipolar regime, Klein tunnelling and Fabry-Pérot interferences, all of which involve electronic transport across p-n junctions. Ballistic snake states propagating along the p-n junctions have been predicted to induce conductance oscillations, manifesting their twisting nature. However, transport studies along p-n junctions have so far only been performed in low mobility devices. Here, we report the observation of conductance oscillations due to ballistic snake states along a p-n interface in high-quality graphene encapsulated by hexagonal boron nitride. These snake states are exceptionally robust as they can propagate over 12 μm, limited only by the size of our sample, and survive up to at least 120 K. The ability to guide carriers over a long distance provide a crucial building block for graphene-based electron optics.
Collapse
|
26
|
Amet F, Bestwick AJ, Williams JR, Balicas L, Watanabe K, Taniguchi T, Goldhaber-Gordon D. Composite fermions and broken symmetries in graphene. Nat Commun 2015; 6:5838. [DOI: 10.1038/ncomms6838] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 11/13/2014] [Indexed: 11/09/2022] Open
|
27
|
Lin X, Du R, Xie X. Recent experimental progress of fractional quantum Hall effect: 5/2 filling state and graphene. Natl Sci Rev 2014. [DOI: 10.1093/nsr/nwu071] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
The phenomenon of fractional quantum Hall effect (FQHE) was first experimentally observed 33 years ago. FQHE involves strong Coulomb interactions and correlations among the electrons, which leads to quasiparticles with fractional elementary charge. Three decades later, the field of FQHE is still active with new discoveries and new technical developments. A significant portion of attention in FQHE has been dedicated to filling factor 5/2 state, for its unusual even denominator and possible application in topological quantum computation. Traditionally, FQHE has been observed in high-mobility GaAs heterostructure, but new materials such as graphene also open up a new area for FQHE. This review focuses on recent progress of FQHE at 5/2 state and FQHE in graphene.
Collapse
Affiliation(s)
- Xi Lin
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Ruirui Du
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Xincheng Xie
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| |
Collapse
|
28
|
Varlet A, Bischoff D, Simonet P, Watanabe K, Taniguchi T, Ihn T, Ensslin K, Mucha-Kruczyński M, Fal'ko VI. Anomalous sequence of quantum Hall liquids revealing a tunable Lifshitz transition in bilayer graphene. PHYSICAL REVIEW LETTERS 2014; 113:116602. [PMID: 25259994 DOI: 10.1103/physrevlett.113.116602] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Indexed: 06/03/2023]
Abstract
Bilayer graphene is a unique system where both the Fermi energy and the low-energy electron dispersion can be tuned. This is brought about by an interplay between trigonal warping and the band gap opened by a transverse electric field. Here, we drive the Lifshitz transition in bilayer graphene to experimentally controllable carrier densities by applying a large transverse electric field to a h-BN-encapsulated bilayer graphene structure. We perform magnetotransport measurements and investigate the different degeneracies in the Landau level spectrum. At low magnetic fields, the observation of filling factors -3 and -6 quantum Hall states reflects the existence of three maxima at the top of the valence-band dispersion. At high magnetic fields, all integer quantum Hall states are observed, indicating that deeper in the valence band the constant energy contours are singly connected. The fact that we observe ferromagnetic quantum Hall states at odd-integer filling factors testifies to the high quality of our sample. This enables us to identify several phase transitions between correlated quantum Hall states at intermediate magnetic fields, in agreement with the calculated evolution of the Landau level spectrum. The observed evolution of the degeneracies, therefore, reveals the presence of a Lifshitz transition in our system.
Collapse
Affiliation(s)
- Anastasia Varlet
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Dominik Bischoff
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Pauline Simonet
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | | | - Vladimir I Fal'ko
- Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom
| |
Collapse
|