1
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Shchepetilnikov AV, Khisameeva AR, Andreeva SA, Nikolaev GA, Fedotova YV, Reichl C, Wegscheider W, Kukushkin IV. Pseudospin Quantum Hall Ferromagnetism Probed by Electron Spin Resonance. PHYSICAL REVIEW LETTERS 2024; 133:096301. [PMID: 39270201 DOI: 10.1103/physrevlett.133.096301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Revised: 06/21/2024] [Accepted: 07/12/2024] [Indexed: 09/15/2024]
Abstract
We study the effect of the pseudospin ferromagnetism with the aid of an electrically detected electron spin resonance in a wide AlAs quantum well containing a high quality two-dimensional electron system. Here, pseudospin emerges as a two-component degree of freedom, that labels degenerate energy minima in momentum space populated by electrons. The built-in mechanical strain in the sample studied imposes a finite "Zeeman" splitting between the pseudospin "up" and "down" states. Because of the anisotropy of the electron spin splitting we were able to independently measure the electron spin resonances originating from the two in-plane valleys. By analyzing the relative resonance amplitudes, we were able to investigate the ferromagnetic phase transitions taking place at integer filling factors of the quantum Hall effect when the magnetic field is tilted. The pseudospin nature of these transitions is demonstrated.
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Affiliation(s)
| | | | | | | | | | - C Reichl
- Solid State Physics Laboratory, ETH Zurich, Otto-Stern-Weg 1, 8093 Zurich, Switzerland
- Quantum Center, ETH Zurich, CH-8093 Zurich, Switzerland
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2
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Krizman G, Bermejo-Ortiz J, Zakusylo T, Hajlaoui M, Takashiro T, Rosmus M, Olszowska N, Kołodziej JJ, Bauer G, Guldner Y, Springholz G, de Vaulchier LA. Valley-Polarized Quantum Hall Phase in a Strain-Controlled Dirac System. PHYSICAL REVIEW LETTERS 2024; 132:166601. [PMID: 38701448 DOI: 10.1103/physrevlett.132.166601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 02/21/2024] [Accepted: 03/27/2024] [Indexed: 05/05/2024]
Abstract
In multivalley systems, the valley pseudospin offers rich physics going from encoding of information by its polarization (valleytronics), to exploring novel phases of matter when its degeneracy is changed. Here, by strain engineering, we reveal fully valley-polarized quantum Hall phases in the Pb_{1-x}Sn_{x}Se Dirac system. Remarkably, when the valley energy splitting exceeds the fundamental band gap, we observe a "bipolar quantum Hall phase," heralded by the coexistence of hole and electron chiral edge states at distinct valleys in the same quantum well. This suggests that spatially overlaid counterpropagating chiral edge states emerging at different valleys do not interfere with each other.
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Affiliation(s)
- G Krizman
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - J Bermejo-Ortiz
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, 24 rue Lhomond 75005 Paris, France
| | - T Zakusylo
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - M Hajlaoui
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - T Takashiro
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - M Rosmus
- National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Czerwone Maki 98, 30-392 Krakow, Poland
| | - N Olszowska
- National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Czerwone Maki 98, 30-392 Krakow, Poland
| | - J J Kołodziej
- National Synchrotron Radiation Centre SOLARIS, Jagiellonian University, Czerwone Maki 98, 30-392 Krakow, Poland
- Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Krakow, Poland
| | - G Bauer
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - Y Guldner
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, 24 rue Lhomond 75005 Paris, France
| | - G Springholz
- Institut für Halbleiter und Festkörperphysik, Johannes Kepler Universität, Altenberger Strasse 69, 4040 Linz, Austria
| | - L-A de Vaulchier
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, 24 rue Lhomond 75005 Paris, France
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3
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Xiang F, Gupta A, Chaves A, Krix ZE, Watanabe K, Taniguchi T, Fuhrer MS, Peeters FM, Neilson D, Milošević MV, Hamilton AR. Intra-Zero-Energy Landau Level Crossings in Bilayer Graphene at High Electric Fields. NANO LETTERS 2023; 23:9683-9689. [PMID: 37883804 DOI: 10.1021/acs.nanolett.3c01456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2023]
Abstract
The highly tunable band structure of the zero-energy Landau level (zLL) of bilayer graphene makes it an ideal platform for engineering novel quantum states. However, the zero-energy Landau level at high electric fields has remained largely unexplored. Here we present magnetotransport measurements of bilayer graphene in high transverse electric fields. We observe previously undetected Landau level crossings at filling factors ν = -2, 1, and 3 at high electric fields. These crossings provide constraints for theoretical models of the zero-energy Landau level and show that the orbital, valley, and spin character of the quantum Hall states at high electric fields is very different from low electric fields. At high E, new transitions between states at ν = -2 with different orbital and spin polarization can be controlled by the gate bias, while the transitions between ν = 0 → 1 and ν = 2 → 3 show anomalous behavior.
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Affiliation(s)
- Feixiang Xiang
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Abhay Gupta
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Andrey Chaves
- Universidade Federal do Ceará, Departamento de Física, Caixa Postal 6030, 60455-760 Fortaleza, Ceará Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Zeb E Krix
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Kenji Watanabe
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - Michael S Fuhrer
- School of Physics and Astronomy and ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET), Monash University, Clayton, Victoria 3800, Australia
| | - François M Peeters
- Universidade Federal do Ceará, Departamento de Física, Caixa Postal 6030, 60455-760 Fortaleza, Ceará Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - David Neilson
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales, Sydney, New South Wales 2052, Australia
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Milorad V Milošević
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, B-2020 Antwerp, Belgium
| | - Alexander R Hamilton
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, University of New South Wales, Sydney, New South Wales 2052, Australia
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4
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Wijewardena UK, Nanayakkara TR, Kriisa A, Reichl C, Wegscheider W, Mani RG. Size dependence- and induced transformations- of fractional quantum Hall effects under tilted magnetic fields. Sci Rep 2022; 12:19204. [PMID: 36357438 PMCID: PMC9649807 DOI: 10.1038/s41598-022-22812-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Accepted: 10/19/2022] [Indexed: 11/12/2022] Open
Abstract
Two-dimensional electron systems subjected to high transverse magnetic fields can exhibit Fractional Quantum Hall Effects (FQHE). In the GaAs/AlGaAs 2D electron system, a double degeneracy of Landau levels due to electron-spin, is removed by a small Zeeman spin splitting, \documentclass[12pt]{minimal}
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\begin{document}$$g \mu _B B$$\end{document}gμBB, comparable to the correlation energy. Then, a change of the Zeeman splitting relative to the correlation energy can lead to a re-ordering between spin polarized, partially polarized, and unpolarized many body ground states at a constant filling factor. We show here that tuning the spin energy can produce fractionally quantized Hall effect transitions that include both a change in \documentclass[12pt]{minimal}
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\begin{document}$$\nu$$\end{document}ν for the \documentclass[12pt]{minimal}
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\begin{document}$$R_{xx}$$\end{document}Rxx minimum, e.g., from \documentclass[12pt]{minimal}
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\begin{document}$$\nu = 11/7$$\end{document}ν=11/7 to \documentclass[12pt]{minimal}
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\begin{document}$$\nu = 8/5$$\end{document}ν=8/5, and a corresponding change in the \documentclass[12pt]{minimal}
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\begin{document}$$R_{xy}$$\end{document}Rxy, e.g., from \documentclass[12pt]{minimal}
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\begin{document}$$R_{xy}/R_{K} = (11/7)^{-1}$$\end{document}Rxy/RK=(11/7)-1 to \documentclass[12pt]{minimal}
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\begin{document}$$R_{xy}/R_{K} = (8/5)^{-1}$$\end{document}Rxy/RK=(8/5)-1, with increasing tilt angle. Further, we exhibit a striking size dependence in the tilt angle interval for the vanishing of the \documentclass[12pt]{minimal}
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\begin{document}$$\nu = 4/3$$\end{document}ν=4/3 and \documentclass[12pt]{minimal}
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\begin{document}$$\nu = 7/5$$\end{document}ν=7/5 resistance minima, including “avoided crossing” type lineshape characteristics, and observable shifts of \documentclass[12pt]{minimal}
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\begin{document}$$R_{xy}$$\end{document}Rxy at the \documentclass[12pt]{minimal}
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\begin{document}$$R_{xx}$$\end{document}Rxx minima- the latter occurring for \documentclass[12pt]{minimal}
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\begin{document}$$\nu = 4/3, 7/5$$\end{document}ν=4/3,7/5 and the 10/7. The results demonstrate both size dependence and the possibility, not just of competition between different spin polarized states at the same \documentclass[12pt]{minimal}
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\begin{document}$$R_{xy}$$\end{document}Rxy, but also the tilt- or Zeeman-energy-dependent- crossover between distinct FQHE associated with different Hall resistances.
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5
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Ma MK, Wang C, Chung YJ, Pfeiffer LN, West KW, Baldwin KW, Winkler R, Shayegan M. Robust Quantum Hall Ferromagnetism near a Gate-Tuned ν=1 Landau Level Crossing. PHYSICAL REVIEW LETTERS 2022; 129:196801. [PMID: 36399735 DOI: 10.1103/physrevlett.129.196801] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 08/12/2022] [Accepted: 09/29/2022] [Indexed: 06/16/2023]
Abstract
In a low-disorder two-dimensional electron system, when two Landau levels of opposite spin or pseudospin cross at the Fermi level, the dominance of the exchange energy can lead to a ferromagnetic, quantum Hall ground state whose gap is determined by the exchange energy and has skyrmions as its excitations. This is normally achieved via applying either hydrostatic pressure or uniaxial strain. We study here a very high-quality, low-density, two-dimensional hole system, confined to a 30-nm-wide (001) GaAs quantum well, in which the two lowest-energy Landau levels can be gate tuned to cross at and near filling factor ν=1. As we tune the field position of the crossing from one side of ν=1 to the other by changing the hole density, the energy gap for the quantum Hall state at ν=1 remains exceptionally large, and only shows a small dip near the crossing. The gap overall follows a sqrt[B] dependence, expected for the exchange energy. Our data are consistent with a robust quantum Hall ferromagnet as the ground state.
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Affiliation(s)
- Meng K Ma
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Chengyu Wang
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Y J Chung
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - L N Pfeiffer
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - R Winkler
- Department of Physics, Northern Illinois University, DeKalb, Illinois 60115, USA
| | - M Shayegan
- Department of Electrical and Computer Engineering, Princeton University, Princeton, New Jersey 08544, USA
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6
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Abstract
Detection and characterization of a different type of topological excitations, namely the domain wall (DW) skyrmion, has received increasing attention because the DW is ubiquitous from condensed matter to particle physics and cosmology. Here we present experimental evidence for the DW skyrmion as the ground state stabilized by long-range Coulomb interactions in a quantum Hall ferromagnet. We develop an alternative approach using nonlocal resistance measurements together with a local NMR probe to measure the effect of low current-induced dynamic nuclear polarization and thus to characterize the DW under equilibrium conditions. The dependence of nuclear spin relaxation in the DW on temperature, filling factor, quasiparticle localization, and effective magnetic fields allows us to interpret this ground state and its possible phase transitions in terms of Wigner solids of the DW skyrmion. These results demonstrate the importance of studying the intrinsic properties of quantum states that has been largely overlooked. Skyrmions, a topological spin texture, have been found in a variety of magnetic systems, including quantum hall ferromagnets. Here, Yang et al demonstrate the existence of skyrmions in domain walls in a quantum Hall ferromagnet, and suggest that these skyrmions form a 1D Wigner crystal.
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7
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Hossain MS, Ma MK, Villegas-Rosales KA, Chung YJ, Pfeiffer LN, West KW, Baldwin KW, Shayegan M. Spontaneous Valley Polarization of Itinerant Electrons. PHYSICAL REVIEW LETTERS 2021; 127:116601. [PMID: 34558923 DOI: 10.1103/physrevlett.127.116601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Accepted: 07/28/2021] [Indexed: 06/13/2023]
Abstract
Memory or transistor devices based on an electron's spin rather than its charge degree of freedom offer certain distinct advantages and comprise a cornerstone of spintronics. Recent years have witnessed the emergence of a new field, valleytronics, which seeks to exploit an electron's valley index rather than its spin. An important component in this quest would be the ability to control the valley index in a convenient fashion. Here we show that the valley polarization can be switched from zero to 1 by a small reduction in density, simply tuned by a gate bias, in a two-dimensional electron system. This phenomenon, which is akin to Bloch spin ferromagnetism, arises fundamentally as a result of electron-electron interaction in an itinerant, dilute electron system. Essentially, the kinetic energy favors an equal distribution of electrons over the available valleys, whereas the interaction between electrons prefers single-valley occupancy below a critical density. The gate-bias-tuned transition we observe is accompanied by a sudden, twofold change in sample resistance, making the phenomenon of interest for potential valleytronic transistor device applications. Our observation constitutes a quintessential demonstration of valleytronics in a very simple experiment.
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Affiliation(s)
- Md S Hossain
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M K Ma
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K A Villegas-Rosales
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Y J Chung
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - L N Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - M Shayegan
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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8
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Li J, Goryca M, Wilson NP, Stier AV, Xu X, Crooker SA. Spontaneous Valley Polarization of Interacting Carriers in a Monolayer Semiconductor. PHYSICAL REVIEW LETTERS 2020; 125:147602. [PMID: 33064502 DOI: 10.1103/physrevlett.125.147602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 09/09/2020] [Indexed: 06/11/2023]
Abstract
We report magnetoabsorption spectroscopy of gated WSe_{2} monolayers in high magnetic fields up to 60 T. When doped with a 2D Fermi sea of mobile holes, well-resolved sequences of optical transitions are observed in both σ^{±} circular polarizations, which unambiguously and separately indicate the number of filled Landau levels (LLs) in both K and K^{'} valleys. This reveals the interaction-enhanced valley Zeeman energy, which is found to be highly tunable with hole density p. We exploit this tunability to align the LLs in K and K^{'}, and find that the 2D hole gas becomes unstable against small changes in LL filling and can spontaneously valley polarize. These results cannot be understood within a single-particle picture, highlighting the importance of exchange interactions in determining the ground state of 2D carriers in monolayer semiconductors.
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Affiliation(s)
- J Li
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - M Goryca
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - N P Wilson
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - A V Stier
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - X Xu
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
| | - S A Crooker
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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9
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Huang K, Wang P, Pfeiffer LN, West KW, Baldwin KW, Liu Y, Lin X. Resymmetrizing Broken Symmetry with Hydraulic Pressure. PHYSICAL REVIEW LETTERS 2019; 123:206602. [PMID: 31809100 DOI: 10.1103/physrevlett.123.206602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Indexed: 06/10/2023]
Abstract
Recent progress in condensed matter physics, such as for graphene, topological insulators, and Weyl semimetals, often originate from the specific topological symmetries of their lattice structures. Quantum states with different degrees of freedom, e.g., spin, valley, layer, etc., arise from these symmetries, and the coherent superposition of these states form multiple energy subbands. The pseudospin, a concept analogous to the Dirac spinor matrices, is a successful description of such multisubband systems. When the electron-electron interaction dominates, many-body quantum phases arise. They usually have discrete pseudospin polarizations and exhibit sharp phase transitions at certain universal critical pseudospin energy splittings. In this Letter, we present our discovery of hydrostatic-pressure-induced degeneracy between the two lowest Landau levels. This degeneracy is evidenced by the pseudospin polarization transitions of the fragile correlated quantum liquid phases near the Landau level filling factor ν=3/2. Benefitting from the constant hole concentration and the sensitive nature of these transitions, we study the fine-tuning effect of the hydrostatic pressure at the order of 10 μeV, well beyond the meV-level state-of-the-art resolution of other techniques.
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Affiliation(s)
- Ke Huang
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Pengjie Wang
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - L N Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W West
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - Yang Liu
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Xi Lin
- International Center for Quantum Materials, Peking University, Beijing 100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
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10
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Lin J, Han T, Piot BA, Wu Z, Xu S, Long G, An L, Cheung P, Zheng PP, Plochocka P, Dai X, Maude DK, Zhang F, Wang N. Determining Interaction Enhanced Valley Susceptibility in Spin-Valley-Locked MoS 2. NANO LETTERS 2019; 19:1736-1742. [PMID: 30720286 DOI: 10.1021/acs.nanolett.8b04731] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two-dimensional transition metal dichalcogenides (TMDCs) are recently emerged electronic systems with various novel properties, such as spin-valley locking, circular dichroism, valley Hall effect, and superconductivity. The reduced dimensionality and large effective masses further produce unconventional many-body interaction effects. Here we reveal strong interaction effects in the conduction band of MoS2 by transport experiment. We study the massive Dirac electron Landau levels (LL) in high-quality MoS2 samples with field-effect mobilities of 24 000 cm2/(V·s) at 1.2 K. We identify the valley-resolved LLs and low-lying polarized LLs using the Lifshitz-Kosevitch formula. By further tracing the LL crossings in the Landau fan diagram, we unambiguously determine the density-dependent valley susceptibility and the interaction enhanced g-factor from 12.7 to 23.6. Near integer ratios of Zeeman-to-cyclotron energies, we discover LL anticrossings due to the formation of quantum Hall Ising ferromagnets, the valley polarizations of which appear to be reversible by tuning the density or an in-plane magnetic field. Our results provide evidence for many-body interaction effects in the conduction band of MoS2 and establish a fertile ground for exploring strongly correlated phenomena of massive Dirac electrons.
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Affiliation(s)
- Jiangxiazi Lin
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Tianyi Han
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Benjamin A Piot
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL , F-38042 Grenoble , France
| | - Zefei Wu
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Shuigang Xu
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Gen Long
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Liheng An
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Patrick Cheung
- Department of Physics , The University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Peng-Peng Zheng
- Department of Physics , The University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Paulina Plochocka
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL , F-31400 Toulouse , France
| | - Xi Dai
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
| | - Duncan K Maude
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL , F-31400 Toulouse , France
| | - Fan Zhang
- Department of Physics , The University of Texas at Dallas , Richardson , Texas 75080 , United States
| | - Ning Wang
- Department of Physics and Center for Quantum Materials , The Hong Kong University of Science and Technology , Clear Water Bay , Hong Kong , China
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11
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Pisoni R, Kormányos A, Brooks M, Lei Z, Back P, Eich M, Overweg H, Lee Y, Rickhaus P, Watanabe K, Taniguchi T, Imamoglu A, Burkard G, Ihn T, Ensslin K. Interactions and Magnetotransport through Spin-Valley Coupled Landau Levels in Monolayer MoS_{2}. PHYSICAL REVIEW LETTERS 2018; 121:247701. [PMID: 30608765 DOI: 10.1103/physrevlett.121.247701] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Indexed: 06/09/2023]
Abstract
The strong spin-orbit coupling and the broken inversion symmetry in monolayer transition metal dichalcogenides results in spin-valley coupled band structures. Such a band structure leads to novel applications in the fields of electronics and optoelectronics. Density functional theory calculations as well as optical experiments have focused on spin-valley coupling in the valence band. Here we present magnetotransport experiments on high-quality n-type monolayer molybdenum disulphide (MoS_{2}) samples, displaying highly resolved Shubnikov-de Haas oscillations at magnetic fields as low as 2 T. We find the effective mass 0.7m_{e}, about twice as large as theoretically predicted and almost independent of magnetic field and carrier density. We further detect the occupation of the second spin-orbit split band at an energy of about 15 meV, i.e., about a factor of 5 larger than predicted. In addition, we demonstrate an intricate Landau level spectrum arising from a complex interplay between a density-dependent Zeeman splitting and spin- and valley-split Landau levels. These observations, enabled by the high electronic quality of our samples, testify to the importance of interaction effects in the conduction band of monolayer MoS_{2}.
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Affiliation(s)
- Riccardo Pisoni
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Andor Kormányos
- Department of Physics, University of Konstanz, D-78464 Konstanz, Germany
- Department of Physics of Complex Systems, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
| | - Matthew Brooks
- Department of Physics, University of Konstanz, D-78464 Konstanz, Germany
| | - Zijin Lei
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Patrick Back
- Institute of Quantum Electronics, Department of Physics, ETH Zürich, 8093 Zürich, Switzerland
| | - Marius Eich
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Hiske Overweg
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Yongjin Lee
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Peter Rickhaus
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, 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
| | - Atac Imamoglu
- Institute of Quantum Electronics, Department of Physics, ETH Zürich, 8093 Zürich, Switzerland
| | - Guido Burkard
- Department of Physics, University of Konstanz, D-78464 Konstanz, Germany
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
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12
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Falson J, Tabrea D, Zhang D, Sodemann I, Kozuka Y, Tsukazaki A, Kawasaki M, von Klitzing K, Smet JH. A cascade of phase transitions in an orbitally mixed half-filled Landau level. SCIENCE ADVANCES 2018; 4:eaat8742. [PMID: 30225370 PMCID: PMC6140610 DOI: 10.1126/sciadv.aat8742] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Accepted: 08/02/2018] [Indexed: 06/08/2023]
Abstract
Half-filled Landau levels host an emergent Fermi liquid that displays instability toward pairing, culminating in a gapped even-denominator fractional quantum Hall ground state. While this pairing may be probed by tuning the polarization of carriers in competing orbital and spin degrees of freedom, sufficiently high quality platforms offering such tunability remain few. We explore the ground states at filling factor ν = 5/2 in ZnO-based two-dimensional electron systems through a forced intersection of opposing spin branches of Landau levels taking quantum numbers N = 1 and 0. We reveal a cascade of phases with distinct magnetotransport features including a gapped phase polarized in the N = 1 level and a compressible phase in N = 0, along with an unexpected Fermi liquid, a second gapped, and a strongly anisotropic nematic-like phase at intermediate polarizations when the levels are near degeneracy. The phase diagram is produced by analyzing the proximity of the intersecting levels and highlights the excellent reproducibility and controllability that ZnO offers for exploring exotic fractionalized electronic phases.
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Affiliation(s)
- Joseph Falson
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
| | - Daniela Tabrea
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
| | - Ding Zhang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Inti Sodemann
- Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany
| | - Yusuke Kozuka
- Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Tokyo 113-8656, Japan
- Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology, Kawaguchi, Saitama 332-0012, Japan
| | - Atsushi Tsukazaki
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Masashi Kawasaki
- Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
| | - Klaus von Klitzing
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
| | - Jurgen H. Smet
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
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13
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Falson J, Kawasaki M. A review of the quantum Hall effects in MgZnO/ZnO heterostructures. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:056501. [PMID: 29353814 DOI: 10.1088/1361-6633/aaa978] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This review visits recent experimental efforts on high mobility two-dimensional electron systems (2DES) hosted at the Mg x Zn[Formula: see text]O/ZnO heterointerface. We begin with the growth of these samples, and highlight the key characteristics of ozone-assisted molecular beam epitaxy required for their production. The transport characteristics of these structures are found to rival that of traditional semiconductor material systems, as signified by the high electron mobility ([Formula: see text] cm2 Vs-1) and rich quantum Hall features. Owing to a large effective mass and small dielectric constant, interaction effects are an order of magnitude stronger in comparison with the well studied GaAs-based 2DES. The strong correlation physics results in robust Fermi-liquid renormalization of the effective mass and spin susceptibility of carriers, which in turn dictates the parameter space for the quantum Hall effect. Finally, we explore the quantum Hall effect with a particular emphasis on the spin degree of freedom of carriers, and how their large spin splitting allows control of the ground states encountered at ultra-low temperatures within the fractional quantum Hall regime. We discuss in detail the physics of even-denominator fractional quantum Hall states, whose observation and underlying character remain elusive and exotic.
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Affiliation(s)
- Joseph Falson
- Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
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14
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Li J, Tupikov Y, Watanabe K, Taniguchi T, Zhu J. Effective Landau Level Diagram of Bilayer Graphene. PHYSICAL REVIEW LETTERS 2018; 120:047701. [PMID: 29437431 DOI: 10.1103/physrevlett.120.047701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 11/18/2017] [Indexed: 06/08/2023]
Abstract
The E=0 octet of bilayer graphene in the filling factor range of -4<ν<4 is a fertile playground for many-body phenomena, yet a Landau level diagram is missing due to strong interactions and competing quantum degrees of freedom. We combine measurements and modeling to construct an empirical and quantitative spectrum. The single-particlelike diagram incorporates interaction effects effectively and provides a unified framework to understand the occupation sequence, gap energies, and phase transitions observed in the octet. It serves as a new starting point for more sophisticated calculations and experiments.
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Affiliation(s)
- Jing Li
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Yevhen Tupikov
- 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
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15
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Kazakov A, Simion G, Lyanda-Geller Y, Kolkovsky V, Adamus Z, Karczewski G, Wojtowicz T, Rokhinson LP. Mesoscopic Transport in Electrostatically Defined Spin-Full Channels in Quantum Hall Ferromagnets. PHYSICAL REVIEW LETTERS 2017; 119:046803. [PMID: 29341779 DOI: 10.1103/physrevlett.119.046803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Indexed: 06/07/2023]
Abstract
In this work, we use electrostatic control of quantum Hall ferromagnetic transitions in CdMnTe quantum wells to study electron transport through individual domain walls (DWs) induced at a specific location. These DWs are formed due to the hybridization of two counterpropagating edge states with opposite spin polarization. Conduction through DWs is found to be symmetric under magnetic field direction reversal, consistent with the helical nature of these DWs. We observe that long domain walls are in the insulating regime with a localization length of 4-6 μm. In shorter DWs, the resistance saturates to a nonzero value at low temperatures. Mesoscopic resistance fluctuations in a magnetic field are investigated. The theoretical model of transport through impurity states within the gap induced by spin-orbit interactions agrees well with the experimental data. Helical DWs have the required symmetry for the formation of synthetic p-wave superconductors. The achieved electrostatic control of a single helical domain wall is a milestone on the path to their reconfigurable network and ultimately to a demonstration of the braiding of non-Abelian excitations.
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Affiliation(s)
- Aleksandr Kazakov
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
| | - George Simion
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
| | - Yuli Lyanda-Geller
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - Valery Kolkovsky
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland
| | - Zbigniew Adamus
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland
| | - Grzegorz Karczewski
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland
| | - Tomasz Wojtowicz
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland
- International Research Centre MagTop, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland
| | - Leonid P Rokhinson
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
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16
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Lu TM, Tracy LA, Laroche D, Huang SH, Chuang Y, Su YH, Li JY, Liu CW. Density-controlled quantum Hall ferromagnetic transition in a two-dimensional hole system. Sci Rep 2017; 7:2468. [PMID: 28572640 PMCID: PMC5453979 DOI: 10.1038/s41598-017-02757-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 04/18/2017] [Indexed: 11/10/2022] Open
Abstract
Quantum Hall ferromagnetic transitions are typically achieved by increasing the Zeeman energy through in-situ sample rotation, while transitions in systems with pseudo-spin indices can be induced by gate control. We report here a gate-controlled quantum Hall ferromagnetic transition between two real spin states in a conventional two-dimensional system without any in-plane magnetic field. We show that the ratio of the Zeeman splitting to the cyclotron gap in a Ge two-dimensional hole system increases with decreasing density owing to inter-carrier interactions. Below a critical density of ~2.4 × 1010 cm−2, this ratio grows greater than 1, resulting in a ferromagnetic ground state at filling factor ν = 2. At the critical density, a resistance peak due to the formation of microscopic domains of opposite spin orientations is observed. Such gate-controlled spin-polarizations in the quantum Hall regime opens the door to realizing Majorana modes using two-dimensional systems in conventional, low-spin-orbit-coupling semiconductors.
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Affiliation(s)
- T M Lu
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA.
| | - L A Tracy
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
| | - D Laroche
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
| | - S-H Huang
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - Y Chuang
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - Y-H Su
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - J-Y Li
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - C W Liu
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
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17
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Yang K, Nagase K, Hirayama Y, Mishima TD, Santos MB, Liu H. Role of chiral quantum Hall edge states in nuclear spin polarization. Nat Commun 2017; 8:15084. [PMID: 28425462 PMCID: PMC5411482 DOI: 10.1038/ncomms15084] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 02/22/2017] [Indexed: 11/09/2022] Open
Abstract
Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in QHF. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response. These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques. Quantum Hall phases in two-dimensional systems have chiral edges, along which electrons propagate in one direction without backscattering. Here, the authors use nuclear magnetic resonance to demonstrate how chiral modes establish dynamical nuclear polarization in a quantum Hall ferromagnet.
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Affiliation(s)
- Kaifeng Yang
- State Key Lab of Superhard Materials, Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
| | - Katsumi Nagase
- Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan
| | - Yoshiro Hirayama
- Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan
| | - Tetsuya D Mishima
- Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks, Norman, Oklahoma 73019-2061, USA
| | - Michael B Santos
- Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks, Norman, Oklahoma 73019-2061, USA
| | - Hongwu Liu
- State Key Lab of Superhard Materials, Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
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18
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Datta B, Dey S, Samanta A, Agarwal H, Borah A, Watanabe K, Taniguchi T, Sensarma R, Deshmukh MM. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene. Nat Commun 2017; 8:14518. [PMID: 28216666 PMCID: PMC5321728 DOI: 10.1038/ncomms14518] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 01/06/2017] [Indexed: 11/09/2022] Open
Abstract
Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm2 V−1 s−1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree–Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field. Few-layered graphene offers a powerful platform to investigate electronic interactions beyond the non-interacting electron picture approximation. Here, the authors report the signature of strong electronic interactions and quantum Hall ferromagnetism in trilayer graphene with ABA stacking.
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Affiliation(s)
- Biswajit Datta
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Santanu Dey
- Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Abhisek Samanta
- Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Hitesh Agarwal
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Abhinandan Borah
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - 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
| | - Rajdeep Sensarma
- Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Mandar M Deshmukh
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
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19
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Miyamoto S, Miura T, Watanabe S, Nagase K, Hirayama Y. Localized NMR Mediated by Electrical-Field-Induced Domain Wall Oscillation in Quantum-Hall-Ferromagnet Nanowire. NANO LETTERS 2016; 16:1596-1601. [PMID: 26885703 DOI: 10.1021/acs.nanolett.5b04209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present fractional quantum Hall domain walls confined in a gate-defined wire structure. Our experiments utilize spatial oscillation of domain walls driven by radio frequency electric fields to cause nuclear magnetic resonance. The resulting spectra are discussed in terms of both large quadrupole fields created around the wire and hyperfine fields associated with the oscillating domain walls. This provides the experimental fact that the domain walls survive near the confined geometry despite of potential deformation, by which a localized magnetic resonance is allowed in electrical means.
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Affiliation(s)
- S Miyamoto
- Department of Physics, Tohoku University , 6-3 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8578, Japan
| | - T Miura
- Department of Physics, Tohoku University , 6-3 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8578, Japan
| | - S Watanabe
- Institute of Science and Engineering, Kanazawa University , Kanazawa 920-1192, Japan
| | - K Nagase
- Department of Physics, Tohoku University , 6-3 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8578, Japan
| | - Y Hirayama
- Department of Physics, Tohoku University , 6-3 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8578, Japan
- WPI-AIMR, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
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20
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Masuda H, Sakai H, Tokunaga M, Yamasaki Y, Miyake A, Shiogai J, Nakamura S, Awaji S, Tsukazaki A, Nakao H, Murakami Y, Arima TH, Tokura Y, Ishiwata S. Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions. SCIENCE ADVANCES 2016; 2:e1501117. [PMID: 27152326 PMCID: PMC4846431 DOI: 10.1126/sciadv.1501117] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/24/2015] [Indexed: 05/23/2023]
Abstract
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.
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Affiliation(s)
- Hidetoshi Masuda
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
| | - Hideaki Sakai
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
- Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Masashi Tokunaga
- The Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
| | - Yuichi Yamasaki
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - Atsushi Miyake
- The Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
| | - Junichi Shiogai
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Shintaro Nakamura
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Satoshi Awaji
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Atsushi Tsukazaki
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Hironori Nakao
- Condensed Matter Research Center and Photon Factory, Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan
| | - Youichi Murakami
- Condensed Matter Research Center and Photon Factory, Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan
| | - Taka-hisa Arima
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561, Japan
| | - Yoshinori Tokura
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - Shintaro Ishiwata
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
- PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
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21
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Archer AC, Jain JK. Phase diagram of the two-component fractional quantum Hall effect. PHYSICAL REVIEW LETTERS 2013; 110:246801. [PMID: 25165951 DOI: 10.1103/physrevlett.110.246801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Indexed: 06/03/2023]
Abstract
We calculate the phase diagram of the two component fractional quantum Hall effect as a function of the spin or valley Zeeman energy and the filling factor, which reveals new phase transitions and phase boundaries spanning many fractional plateaus. This phase diagram is relevant to the fractional quantum Hall effect in graphene and in GaAs and AlAs quantum wells, when either the spin or valley degree of freedom is active.
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Affiliation(s)
- Alexander C Archer
- Department of Physics, 104 Davey Lab, Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Jainendra K Jain
- Department of Physics, 104 Davey Lab, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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22
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Hwang HY, Iwasa Y, Kawasaki M, Keimer B, Nagaosa N, Tokura Y. Emergent phenomena at oxide interfaces. NATURE MATERIALS 2012; 11:103-13. [PMID: 22270825 DOI: 10.1038/nmat3223] [Citation(s) in RCA: 725] [Impact Index Per Article: 60.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Recent technical advances in the atomic-scale synthesis of oxide heterostructures have provided a fertile new ground for creating novel states at their interfaces. Different symmetry constraints can be used to design structures exhibiting phenomena not found in the bulk constituents. A characteristic feature is the reconstruction of the charge, spin and orbital states at interfaces on the nanometre scale. Examples such as interface superconductivity, magneto-electric coupling, and the quantum Hall effect in oxide heterostructures are representative of the scientific and technological opportunities in this rapidly emerging field.
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Affiliation(s)
- H Y Hwang
- Correlated Electron Research Group, RIKEN-Advanced Science Institute, Saitama 351-0198, Japan.
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23
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Ferreira GJ, Freire HJP, Egues JC. Many-body effects on the rho(xx) ringlike structures in two-subband wells. PHYSICAL REVIEW LETTERS 2010; 104:066803. [PMID: 20366846 DOI: 10.1103/physrevlett.104.066803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Indexed: 05/29/2023]
Abstract
The longitudinal resistivity rho(xx) of two-dimensional electron gases formed in wells with two subbands displays ringlike structures when plotted in a density-magnetic-field diagram, due to the crossings of spin-split Landau levels (LLs) from distinct subbands. Using spin density functional theory and linear response, we investigate the shape and spin polarization of these structures as a function of temperature and magnetic-field tilt angle. We find that (i) some of the rings "break" at sufficiently low temperatures due to a quantum Hall ferromagnetic phase transition, thus exhibiting a high degree of spin polarization (approximately 50%) within, consistent with the NMR data of Zhang et al. [Phys. Rev. Lett. 98, 246802 (2007)], and (ii) for increasing tilting angles the interplay between the anticrossings due to inter-LL couplings and the exchange-correlation effects leads to a collapse of the rings at some critical angle theta(c), in agreement with the data of Guo et al. [Phys. Rev. B 78, 233305 (2008)].
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Affiliation(s)
- Gerson J Ferreira
- Departamento de Física e Informática, Instituto de Física de São Carlos, Universidade de São Paulo, 13560-970 São Carlos, São Paulo, Brazil
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24
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Abergel DSL, Chakraborty T. Long-range Coulomb interaction in bilayer graphene. PHYSICAL REVIEW LETTERS 2009; 102:056807. [PMID: 19257539 DOI: 10.1103/physrevlett.102.056807] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Indexed: 05/27/2023]
Abstract
We report on our studies of interacting electrons in bilayer graphene in a magnetic field. We demonstrate that the long-range Coulomb interactions between electrons in this material are highly important and account for the band asymmetry in recent optical magneto-absorption experiments [E. A. Henriksen, Phys. Rev. Lett. 100, 087403 (2008)10.1103/PhysRevLett.100.087403]. We show that in the unbiased bilayer (where both layers are at the same electrostatic potential), the interactions can cause mixing of Landau levels in moderate magnetic fields. For the biased bilayer (when the two layers are at different potentials), we demonstrate that the interactions are responsible for a change in the total spin of the ground state for half-filled Landau levels in the valence band.
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Affiliation(s)
- D S L Abergel
- Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
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25
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Gokmen T, Padmanabhan M, Shayegan M. Dependence of effective mass on spin and valley degrees of freedom. PHYSICAL REVIEW LETTERS 2008; 101:146405. [PMID: 18851552 DOI: 10.1103/physrevlett.101.146405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Indexed: 05/26/2023]
Abstract
We measure the effective mass (m) of interacting two-dimensional electrons confined to an AlAs quantum well while we change the conduction-band valley occupation and the spin polarization via the application of strain and magnetic field, respectively. Compared to its band value, m is enhanced unless the electrons are fully valley- and spin-polarized. Incidentally, in the fully spin- and valley-polarized regime, the electron system exhibits an insulating behavior.
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Affiliation(s)
- T Gokmen
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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26
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Toyama K, Nishioka T, Sawano K, Shiraki Y, Okamoto T. Electronic transport properties of the Ising quantum Hall ferromagnet in a Si quantum well. PHYSICAL REVIEW LETTERS 2008; 101:016805. [PMID: 18764140 DOI: 10.1103/physrevlett.101.016805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Indexed: 05/26/2023]
Abstract
Magnetotransport properties are investigated for a high mobility Si two-dimensional electron system in the vicinity of a Landau level crossing point. At low temperatures, the resistance peak having a strong anisotropy shows large hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak is split into two peaks in the paramagnetic regime. A mean field calculation for the peak positions indicates that electron scattering is strong when the pseudospin is partially polarized. We also study the current-voltage characteristics which exhibit a wide voltage plateau.
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Affiliation(s)
- Kiyohiko Toyama
- Department of Physics, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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27
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Khrapai VS, Shashkin AA, Trokina MG, Dolgopolov VT, Pellegrini V, Beltram F, Biasiol G, Sorba L. Direct measurements of fractional quantum Hall effect gaps. PHYSICAL REVIEW LETTERS 2007; 99:086802. [PMID: 17930970 DOI: 10.1103/physrevlett.99.086802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Indexed: 05/25/2023]
Abstract
We measure the chemical potential jump across the fractional gap in the low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs single heterojunctions. In the fully spin-polarized regime, the gap for filling factor nu=1/3 increases linearly with the magnetic field and is coincident with that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau level. In low magnetic fields, at the ground-state spin transition for nu=2/3, a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed.
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Affiliation(s)
- V S Khrapai
- Institute of Solid State Physics, Chernogolovka, Moscow District, Russia
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28
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Takashina K, Brun M, Ota T, Maude DK, Fujiwara A, Ono Y, Takahashi Y, Hirayama Y. Anomalous resistance ridges along filling factor nu=4i. PHYSICAL REVIEW LETTERS 2007; 99:036803. [PMID: 17678309 DOI: 10.1103/physrevlett.99.036803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Indexed: 05/16/2023]
Abstract
We report anomalous structure in the magnetoresistance of SiO(2)/Si(100)/SiO(2) quantum wells. When Landau levels of opposite valleys are driven through coincidence at the Fermi level, the longitudinal resistance displays elevations at filling factors that are integer multiples of 4 (nu=4i) accompanied by suppression on either side of nu=4i. This persists when either the magnetic field or the valley splitting is swept, leading to resistance ridges running along nu=4i. The range of field over which they are observed points to the role of spin degeneracy, which is directly confirmed by their disappearance with the addition of an in-plane magnetic field. The data suggest a new type of many-body effect arising from the combined degeneracy due to the valley and the spin degrees of freedom.
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Affiliation(s)
- K Takashina
- NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198, Japan
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29
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Freire HJP, Egues JC. Hysteretic resistance spikes in quantum hall ferromagnets without domains. PHYSICAL REVIEW LETTERS 2007; 99:026801. [PMID: 17678243 DOI: 10.1103/physrevlett.99.026801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Indexed: 05/16/2023]
Abstract
We use spin-density-functional theory to study recently reported hysteretic magnetoresistance rho(xx) spikes in Mn-based 2D electron gases [Phys. Rev. Lett. 89, 266802 (2002)10.1103/PhysRevLett.89.266802]. We find hysteresis loops in our calculated Landau fan diagrams and total energies signaling quantum Hall ferromagnet phase transitions. Spin-dependent exchange-correlation effects are crucial to stabilize the relevant magnetic phases arising from distinct symmetry-broken excited- and ground-state solutions of the Kohn-Sham equations. Besides hysteretic spikes in rho(xx), we predict hysteretic dips in the Hall resistance rho(xy). Our theory, without domain walls, satisfactorily explains the recent data.
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Affiliation(s)
- Henrique J P Freire
- Departamento de Física e Informática, Instituto de Física de São Carlos, Universidade de São Paulo, 13560-970 São Carlos, São Paulo, Brazil
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30
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Abstract
Resistively detected nuclear spin relaxation measurements in closely separated two-dimensional electron systems reveal strong low-frequency electron-spin fluctuations in the quantum Hall regime. As the temperature is decreased, the spin fluctuations, manifested by a sharp enhancement of the nuclear spin-lattice relaxation rate 1/T1, continue to grow down to the lowest temperature of 66 millikelvin. The observed divergent behavior of 1/T1 signals a gapless spin excitation mode and is a hallmark of canted antiferromagnetic order. Our data demonstrate the realization of a two-dimensional system with planar broken symmetry, in which fluctuations do not freeze out when approaching the zero temperature limit.
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Affiliation(s)
- Norio Kumada
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
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31
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Lai K, Pan W, Tsui DC, Lyon S, Mühlberger M, Schäffler F. Intervalley gap anomaly of two-dimensional electrons in silicon. PHYSICAL REVIEW LETTERS 2006; 96:076805. [PMID: 16606125 DOI: 10.1103/physrevlett.96.076805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Indexed: 05/08/2023]
Abstract
We report here a systematic study of the energy gaps at the odd-integer quantum Hall states nu = 3 and 5 under tilted magnetic (B) fields in a high quality Si two-dimensional electron system. Out of the coincidence region, the valley splitting is independent of the in-plane fields. However, the nu = 3 valley gap differs by about a factor of 3 (Deltav approximately 0.4 vs 1.2 K) on different sides of the coincidence. More surprisingly, instead of reducing to zero, the energy gaps at nu = 3 and 5 rise rapidly when approaching the coincidence angles. We believe that such an anomaly is related to strong couplings of the nearly degenerate Landau levels.
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Affiliation(s)
- K Lai
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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32
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Vakili K, Shkolnikov YP, Tutuc E, Bishop NC, De Poortere EP, Shayegan M. Spin-dependent resistivity at transitions between integer quantum hall states. PHYSICAL REVIEW LETTERS 2005; 94:176402. [PMID: 15904319 DOI: 10.1103/physrevlett.94.176402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2004] [Indexed: 05/02/2023]
Abstract
The longitudinal resistivity at transitions between integer quantum Hall states in two-dimensional electrons confined to AlAs quantum wells is found to depend on the spin orientation of the partially filled Landau level in which the Fermi energy resides. The resistivity can be enhanced by an order of magnitude as the spin orientation of this energy level is aligned with the majority spin. We discuss possible causes and suggest a new explanation for the spikelike features observed at the edges of quantum Hall minima near Landau level crossings.
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Affiliation(s)
- K Vakili
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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33
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Perry RS, Kitagawa K, Grigera SA, Borzi RA, Mackenzie AP, Ishida K, Maeno Y. Multiple first-order metamagnetic transitions and quantum oscillations in ultrapure Sr3Ru2O7. PHYSICAL REVIEW LETTERS 2004; 92:166602. [PMID: 15169251 DOI: 10.1103/physrevlett.92.166602] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2003] [Indexed: 05/24/2023]
Abstract
We present measurements on ultraclean single crystals of the bilayered ruthenate metal Sr3Ru2O7, which has a magnetic-field-tuned quantum critical point. Quantum oscillations of differing frequencies can be seen in the resistivity both below and above its metamagnetic transition. This frequency shift corresponds to a small change in the Fermi surface volume that is qualitatively consistent with the small moment change in the magnetization across the metamagnetic transition. Very near the metamagnetic field, unusual behavior is seen. There is a strong enhancement of the resistivity in a narrow field window, with a minimum in the resistivity as a function of temperature below 1 K that becomes more pronounced as the disorder level decreases. The region of anomalous behavior is bounded at low temperatures by two first-order phase transitions. The implications of the results are discussed.
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Affiliation(s)
- R S Perry
- Kyoto University International Innovation Center, Kyoto 606-8501, Japan
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34
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De Poortere EP, Tutuc E, Shayegan M. Critical resistance in the AlAs quantum Hall ferromagnet. PHYSICAL REVIEW LETTERS 2003; 91:216802. [PMID: 14683327 DOI: 10.1103/physrevlett.91.216802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2003] [Indexed: 05/24/2023]
Abstract
Magnetic transitions in AlAs two-dimensional electrons give rise to sharp resistance spikes within the quantum Hall effect. Such spikes are likely caused by carrier scattering at magnetic domain walls below the Curie temperature. We report a critical behavior in the temperature dependence of the spike width and amplitude, from which we deduce the Curie temperature of the quantum Hall ferromagnet. Our data also reveal that the Curie temperature increases monotonically with carrier density.
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Affiliation(s)
- E P De Poortere
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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35
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Chen M, Kang W, Wegscheider W. Metamorphosis of the quantum Hall ferromagnet at nu=2/5. PHYSICAL REVIEW LETTERS 2003; 91:116804. [PMID: 14525452 DOI: 10.1103/physrevlett.91.116804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2002] [Indexed: 05/24/2023]
Abstract
We report on the dramatic evolution of the quantum Hall ferromagnet in the fractional quantum Hall regime at nu=2/5 filling. A large enhancement in the characteristic time scale gives rise to a dynamical transition into a novel quantized Hall state. The observed Hall state is determined to be a zero-temperature phase distinct from the spin-polarized and spin-unpolarized nu=2/5 fractional quantum Hall states. It is characterized by a strong temperature dependence and puzzling correlation between temperature and time.
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Affiliation(s)
- Michelle Chen
- James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA
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36
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Jaroszyński J, Andrearczyk T, Karczewski G, Wróbel J, Wojtowicz T, Papis E, Kamińska E, Piotrowska A, Popović D, Dietl T. Ising quantum Hall ferromagnet in magnetically doped quantum wells. PHYSICAL REVIEW LETTERS 2002; 89:266802. [PMID: 12484847 DOI: 10.1103/physrevlett.89.266802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2002] [Indexed: 05/24/2023]
Abstract
We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T(C) as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance "spikes" at T-->T(C) corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.
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Affiliation(s)
- J Jaroszyński
- Institute of Physics, Polish Academy of Sciences, aleja Lotników 32/46, 02-668 Warszawa, Poland.
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37
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Avishai Y, Meir Y. New spin-orbit-induced universality class in the integer quantum Hall regime. PHYSICAL REVIEW LETTERS 2002; 89:076602. [PMID: 12190544 DOI: 10.1103/physrevlett.89.076602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2001] [Indexed: 05/23/2023]
Abstract
Using heuristic arguments and numerical simulations it is argued that the critical exponent nu describing the localization length divergence at the integer quantum-Hall transition is modified in the presence of spin-orbit scattering with short-range correlations. The exponent is very close to nu=4/3, the percolation correlation length exponent, consistent with the prediction of a semiclassical argument. In addition, a band of weakly localized states is conjectured.
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Affiliation(s)
- Yshai Avishai
- Department of Physics and Ilse Katz Center for Meso- and Nanoscale Science and Technology, Ben Gurion University, Beer Sheva, Israel
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38
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Smet JH, Deutschmann RA, Ertl F, Wegscheider W, Abstreiter G, von Klitzing K. Gate-voltage control of spin interactions between electrons and nuclei in a semiconductor. Nature 2002; 415:281-6. [PMID: 11796998 DOI: 10.1038/415281a] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Semiconductors are ubiquitous in device electronics, because their charge distributions can be conveniently manipulated with voltages to perform logic operations. Achieving a similar level of control over the spin degrees of freedom, either from electrons or nuclei, could provide intriguing prospects for both information processing and the study of fundamental solid-state physics issues. Here we report procedures that carry out the controlled transfer of spin angular momentum between electrons-confined to two dimensions and subjected to a perpendicular magnetic field-and the nuclei of the host semiconductor, using gate voltages only. We show that the spin transfer rate can be enhanced near a ferromagnetic ground state of the electron system, and that the induced nuclear spin polarization can be subsequently stored and 'read out'. These techniques can also be combined into a spectroscopic tool to detect the low-energy collective excitations in the electron system that promote the spin transfer. The existence of such excitations is contingent on appropriate electron-electron correlations, and these can be tuned by changing, for example, the electron density via a gate voltage.
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Affiliation(s)
- J H Smet
- Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
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39
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Salis G, Kato Y, Ensslin K, Driscoll DC, Gossard AC, Awschalom DD. Electrical control of spin coherence in semiconductor nanostructures. Nature 2001; 414:619-22. [PMID: 11740554 DOI: 10.1038/414619a] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The processing of quantum information based on the electron spin degree of freedom requires fast and coherent manipulation of local spins. One approach is to provide spatially selective tuning of the spin splitting--which depends on the g-factor--by using magnetic fields, but this requires their precise control at reduced length scales. Alternative proposals employ electrical gating and spin engineering in semiconductor heterostructures involving materials with different g-factors. Here we show that spin coherence can be controlled in a specially designed AlxGa1-xAs quantum well in which the Al concentration x is gradually varied across the structure. Application of an electric field leads to a displacement of the electron wavefunction within the quantum well, and because the electron g-factor varies strongly with x, the spin splitting is therefore also changed. Using time-resolved optical techniques, we demonstrate gate-voltage-mediated control of coherent spin precession over a 13-GHz frequency range in a fixed magnetic field of 6 T, including complete suppression of precession, reversal of the sign of g, and operation up to room temperature.
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Affiliation(s)
- G Salis
- Center for Spintronics and Quantum Computing, University of California, Santa Barbara, California 93106, USA
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40
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Jungwirth T, MacDonald AH. Resistance spikes and domain wall loops in Ising quantum Hall ferromagnets. PHYSICAL REVIEW LETTERS 2001; 87:216801. [PMID: 11736361 DOI: 10.1103/physrevlett.87.216801] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2001] [Indexed: 05/23/2023]
Abstract
We explain the recent observation of resistance spikes and hysteretic transport properties in Ising quantum Hall ferromagnets in terms of the unique physics of their domain walls. Self-consistent RPA/Hartree-Fock theory is applied to microscopically determine properties of the ground state and domain wall excitations. In these systems domain wall loops support one-dimensional electron systems with an effective mass comparable to the bare electron mass and may carry charge. Our theory is able to account quantitatively for the experimental Ising critical temperature and to explain qualitative characteristics of the resistive hysteresis loops.
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Affiliation(s)
- T Jungwirth
- Department of Physics, The University of Texas, Austin, Texas 78712 and Institute of Physics ASCR, Cukrovarnická 10, 162 53 Praha 6, Czech Republic
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41
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Muraki K, Saku T, Hirayama Y. Charge excitations in easy-axis and easy-plane quantum Hall ferromagnets. PHYSICAL REVIEW LETTERS 2001; 87:196801. [PMID: 11690439 DOI: 10.1103/physrevlett.87.196801] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2001] [Indexed: 05/23/2023]
Abstract
We study charge excitations in quantum Hall ferromagnets realized in a symmetric quantum well. Landau levels (LLs) with different subband and orbital indices crossing at the Fermi level act as up and down pseudospin levels. The activation energy measured as a function of the pseudospin Zeeman energy, Delta(Z), reveals easy-plane and easy-axis ferromagnetism for LL filling of nu = 3 and 4, respectively, for which the crossing levels have parallel and antiparallel spin. For nu = 4, we observe a sharp reduction in the gap for Delta(Z)-->0, which we discuss in terms of a topological excitation in domain walls akin to Skyrmions.
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Affiliation(s)
- K Muraki
- NTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
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