1
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Pu S, Balram AC, Taylor J, Fradkin E, Papić Z. Microscopic Model for Fractional Quantum Hall Nematics. PHYSICAL REVIEW LETTERS 2024; 132:236503. [PMID: 38905694 DOI: 10.1103/physrevlett.132.236503] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Accepted: 04/25/2024] [Indexed: 06/23/2024]
Abstract
Geometric fluctuations of the density mode in a fractional quantum Hall (FQH) state can give rise to a nematic FQH phase, a topological state with a spontaneously broken rotational symmetry. While experiments on FQH states in the second Landau level have reported signatures of putative FQH nematics in anisotropic transport, a realistic model for this state has been lacking. We show that the standard model of particles in the lowest Landau level interacting via the Coulomb potential realizes the FQH nematic transition, which is reached by a progressive reduction of the strength of the shortest-range Haldane pseudopotential. Using exact diagonalization and variational wave functions, we demonstrate that the FQH nematic transition occurs when the system's neutral gap closes in the long-wavelength limit while the charge gap remains open. We confirm the symmetry-breaking nature of the transition by demonstrating the existence of a "circular moat" potential in the manifold of states with broken rotational symmetry, while its geometric character is revealed through the strong fluctuations of the nematic susceptibility and Hall viscosity.
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Affiliation(s)
| | | | | | - Eduardo Fradkin
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA
- Anthony J. Leggett Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA
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2
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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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3
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Lupatini M, Knüppel P, Faelt S, Winkler R, Shayegan M, Imamoglu A, Wegscheider W. Spin Reversal of a Quantum Hall Ferromagnet at a Landau Level Crossing. PHYSICAL REVIEW LETTERS 2020; 125:067404. [PMID: 32845701 DOI: 10.1103/physrevlett.125.067404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 06/22/2020] [Indexed: 06/11/2023]
Abstract
When Landau levels (LLs) become degenerate near the Fermi energy in the quantum Hall regime, interaction effects can drastically modify the electronic ground state. We study the quantum Hall ferromagnet formed in a two-dimensional hole gas around the LL filling factor ν=1 in the vicinity of a LL crossing in the heave-hole valence band. Cavity spectroscopy in the strong-coupling regime allows us to optically extract the spin polarization of the two-dimensional hole gas. By analyzing this polarization as a function of hole density and magnetic field, we observe a spin flip of the ferromagnet. Furthermore, the depolarization away from ν=1 accelerates close to the LL crossing. This is indicative of an increase in the size of skyrmion excitations as the effective Zeeman energy vanishes at the LL crossing.
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Affiliation(s)
- M Lupatini
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - P Knüppel
- Institute of Quantum Electronics, ETH Zürich, CH-8093, Zürich, Switzerland
| | - S Faelt
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
- Institute of Quantum Electronics, ETH Zürich, CH-8093, Zürich, Switzerland
| | - R Winkler
- Department of Physics, Northern Illinois University, DeKalb, Illinois 60115, USA and Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - M Shayegan
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
| | - A Imamoglu
- Institute of Quantum Electronics, ETH Zürich, CH-8093, Zürich, Switzerland
| | - W Wegscheider
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
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4
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Pan W, Reno JL, Reyes AP. Enhanced stability of quantum Hall skyrmions under radio-frequency radiations. Sci Rep 2020; 10:7659. [PMID: 32376887 PMCID: PMC7203198 DOI: 10.1038/s41598-020-64505-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 04/17/2020] [Indexed: 11/09/2022] Open
Abstract
We present in this paper the results from a recent study on the stability of the quantum Hall skyrmions state at a Landau level filling factor (ν) close to ν = 1 in a narrow GaAs quantum well. Consistent with previous work, a resonant behavior is observed in the resistively detected NMR measurements. In the subsequent current-voltage (I-V) measurements to examine its breakdown behavior under radio frequency radiations, we observe that the critical current assumes the largest value right at the 75As nuclear resonant frequency. We discuss possible origin for this unexpectedly enhanced stability.
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Affiliation(s)
- W Pan
- Sandia National Laboratories, Livermore, California, USA.
| | - J L Reno
- Sandia National Laboratories, Albuquerque, New Mexico, USA
| | - A P Reyes
- National High Magnetic Field Laboratory, Tallahassee, Florida, USA
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5
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Dickmann S. Spin-rotation mode in a quantum Hall ferromagnet. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:015603. [PMID: 31491770 DOI: 10.1088/1361-648x/ab4230] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A spin-rotation mode emerging in a quantum Hall ferromagnet due to laser pulse excitation is studied. This state, macroscopically representing a rotation of the entire electron spin-system to a certain angle, is not microscopically equivalent to a coherent turn of all spins as a single-whole and is presented in the form of a combination of eigen quantum states corresponding to all possible S z spin numbers. The motion of the macroscopic quantum state is studied microscopically by solving a non-stationary Schrödinger equation and by means of a kinetic approach where damping of the spin-rotation mode is related to an elementary process, namely, transformation of a 'Goldstone spin exciton' to a 'spin-wave exciton'. The system exhibits a spin stochastization mechanism (determined by spatial fluctuations of the Landé factor) ensuring damping, transverse spin relaxation, but irrelevant to decay of spin-wave excitons and thus not involving longitudinal relaxation, i.e. recovery of the S z number to its equilibrium value.
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Affiliation(s)
- S Dickmann
- Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, 142432, Russia
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6
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Luo HB, Li L, Liu WM. Three-Dimensional Skyrmions with Arbitrary Topological Number in a Ferromagnetic Spin-1 Bose-Einstein Condensate. Sci Rep 2019; 9:18804. [PMID: 31827109 PMCID: PMC6906496 DOI: 10.1038/s41598-019-54856-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 11/15/2019] [Indexed: 12/03/2022] Open
Abstract
We propose a new scheme for creating three-dimensional Skyrmions in a ferromagnetic spin-1 Bose-Einstein condensate by manipulating a multipole magnetic field and a pair of counter-propagating laser beams. The result shows that a three-dimensional Skyrmion with topological number Q = 2 can be created by a sextupole magnetic field and the laser beams. Meanwhile, the vortex ring and knot structure in the Skyrmion are found. The topological number can be calculated analytically in our model, which implies that the method can be extended to create Skyrmions with arbitrary topological number. As the examples, three-dimensional Skyrmions with Q = 3, 4 are also demonstrated and are distinguishable by the density distributions with a specific quantization axis. These topological objects have the potential to be realized in ferromagnetic spin-1 Bose-Einstein condensates experimentally.
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Affiliation(s)
- Huan-Bo Luo
- Institute of Theoretical Physics, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan, 030006, China
| | - Lu Li
- Institute of Theoretical Physics, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan, 030006, China
| | - Wu-Ming Liu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
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7
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Parameswaran SA, Feldman BE. Quantum Hall valley nematics. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:273001. [PMID: 30743251 DOI: 10.1088/1361-648x/ab0636] [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
Two-dimensional electron gases in strong magnetic fields provide a canonical platform for realizing a variety of electronic ordering phenomena. Here we review the physics of one intriguing class of interaction-driven quantum Hall states: quantum Hall valley nematics. These phases of matter emerge when the formation of a topologically insulating quantum Hall state is accompanied by the spontaneous breaking of a point-group symmetry that combines a spatial rotation with a permutation of valley indices. The resulting orientational order is particularly sensitive to quenched disorder, while quantum Hall physics links charge conduction to topological defects. We discuss how these combine to yield a rich phase structure, and their implications for transport and spectroscopy measurements. In parallel, we discuss relevant experimental systems. We close with an outlook on future directions.
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Affiliation(s)
- S A Parameswaran
- Rudolf Peierls Centre for Theoretical Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, United Kingdom
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8
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Randeria MT, Agarwal K, Feldman BE, Ding H, Ji H, Cava RJ, Sondhi SL, Parameswaran SA, Yazdani A. Interacting multi-channel topological boundary modes in a quantum Hall valley system. Nature 2019; 566:363-367. [PMID: 30728501 DOI: 10.1038/s41586-019-0913-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Accepted: 11/23/2018] [Indexed: 11/09/2022]
Abstract
Symmetry and topology are central to understanding quantum Hall ferromagnets (QHFMs), two-dimensional electronic phases with spontaneously broken spin or pseudospin symmetry whose wavefunctions also have topological properties1,2. Domain walls between distinct broken-symmetry QHFM phases are predicted to host gapless one-dimensional modes-that is, quantum channels that emerge because of a topological change in the underlying electronic wavefunctions at such interfaces. Although various QHFMs have been identified in different materials3-8, interacting electronic modes at these domain walls have not been probed. Here we use a scanning tunnelling microscope to directly visualize the spontaneous formation of boundary modes at domain walls between QHFM phases with different valley polarization (that is, the occupation of equal-energy but quantum mechanically distinct valleys in the electronic structure) on the surface of bismuth. Spectroscopy shows that these modes occur within a topological energy gap, which closes and reopens as the valley polarization switches across the domain wall. By changing the valley flavour and the number of modes at the domain wall, we can realize different regimes in which the valley-polarized channels are either metallic or develop a spectroscopic gap. This behaviour is a consequence of Coulomb interactions constrained by the valley flavour, which determines whether electrons in the topological modes can backscatter, making these channels a unique class of interacting one-dimensional quantum wires. QHFM domain walls can be realized in different classes of two-dimensional materials, providing the opportunity to explore a rich phase space of interactions in these quantum wires.
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Affiliation(s)
- Mallika T Randeria
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Kartiek Agarwal
- Department of Electrical Engineering, Princeton University, Princeton, NJ, USA
| | - Benjamin E Feldman
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA.,Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, USA.,Department of Physics, Stanford University, Stanford, CA, USA
| | - Hao Ding
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Huiwen Ji
- Department of Chemistry, Princeton University, Princeton, NJ, USA
| | - R J Cava
- Department of Chemistry, Princeton University, Princeton, NJ, USA
| | - S L Sondhi
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | | | - Ali Yazdani
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA.
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9
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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.
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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
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10
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Polshyn H, Zhou H, Spanton EM, Taniguchi T, Watanabe K, Young AF. Quantitative Transport Measurements of Fractional Quantum Hall Energy Gaps in Edgeless Graphene Devices. PHYSICAL REVIEW LETTERS 2018; 121:226801. [PMID: 30547606 DOI: 10.1103/physrevlett.121.226801] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 10/19/2018] [Indexed: 06/09/2023]
Abstract
Owing to their wide tunability, multiple internal degrees of freedom, and low disorder, graphene heterostructures are emerging as a promising experimental platform for fractional quantum Hall (FQH) studies. Here, we report FQH thermal activation gap measurements in dual graphite-gated monolayer graphene devices fabricated in an edgeless Corbino geometry. In devices with substrate-induced sublattice splitting, we find a tunable crossover between single- and multicomponent FQH states in the zero energy Landau level. Activation gaps in the single-component regime show excellent agreement with numerical calculations using a single broadening parameter Γ≈7.2 K. In the first excited Landau level, in contrast, FQH gaps are strongly influenced by Landau level mixing, and we observe an unexpected valley-ordered state at integer filling ν=-4.
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Affiliation(s)
- H Polshyn
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - H Zhou
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - E M Spanton
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - T Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - K Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - A F Young
- Department of Physics, University of California, Santa Barbara, California 93106, USA
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11
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Fukuda JI, Nych A, Ognysta U, Žumer S, Muševič I. Liquid-crystalline half-Skyrmion lattice spotted by Kossel diagrams. Sci Rep 2018; 8:17234. [PMID: 30467358 PMCID: PMC6250727 DOI: 10.1038/s41598-018-35514-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 11/05/2018] [Indexed: 11/09/2022] Open
Abstract
Skyrmions are swirl-like topological entities that have been shown to emerge in various condensed matter systems. Their identification has been carried out in different ways including scattering techniques and real-space observations. Here we show that Kossel diagrams can identify the formation of a hexagonal lattice of half-Skyrmions in a thin film of a chiral liquid crystal, in which case Kossel lines appear as hexagonally arranged circular arcs. Our experimental observations on a hexagonal lattice of half-Skyrmions and other defect structures resembling that of a bulk cholesteric blue phase are perfectly accounted for by numerical calculations and a theoretical argument attributing strong reflections yielding Kossel lines to guided mode resonances in the thin liquid crystal film. Our study demonstrates that a liquid crystal is a model system allowing the investigation of topological entities by various optical means, and also that Kossel techniques are applicable to the investigation of thin systems with non-trivial photonic band structures including topologically protected optical surface states.
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Affiliation(s)
- Jun-Ichi Fukuda
- Department of Physics, Kyushu University, 744, Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
- National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, 305-8568, Japan.
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia.
| | - Andriy Nych
- Department of Molecular Photoelectronics, Institute of Physics, prospect Nauky, 46, Kyiv, 03680, Ukraine.
- Condensed Matter Department, Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.
| | - Uliana Ognysta
- Department of Molecular Photoelectronics, Institute of Physics, prospect Nauky, 46, Kyiv, 03680, Ukraine
- Condensed Matter Department, Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia
| | - Slobodan Žumer
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
- Condensed Matter Department, Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia
| | - Igor Muševič
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
- Condensed Matter Department, Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia
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12
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Fukuda JI, Žumer S. Reflection spectra and near-field images of a liquid crystalline half-Skyrmion lattice. OPTICS EXPRESS 2018; 26:1174-1184. [PMID: 29401994 DOI: 10.1364/oe.26.001174] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 12/21/2017] [Indexed: 06/07/2023]
Abstract
We investigate numerically the optical properties of a hexagonal half-Skyrmion lattice exhibited by a highly chiral liquid crystal confined between two parallel plates. Our study focuses on the near and far-field reflection for normally incident light with different polarizations. We show that, when the wavelength of the incident light is longer than a threshold value, the reflectivity is almost insensitive to the polarization of the incident light, although the intensity profiles of the reflected light, in particular in the near-field regime, depend significantly on the polarization. The former property is attributable to the quasi two-dimensional nature of the half-Skyrmion lattice, that is, almost uniform orientational order along the direction normal to the confining plates. Our results for the intensity of reflected light generated by evanescent as well as propagating contributions suggest that direct evidence of the formation and structure of half-Skyrmions could be provided by near-field optics with resolutions higher than that of conventional optical microscopy.
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13
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Kang S, Lee EW, Li T, Liang X, Tokita M, Nakajima K, Watanabe J. Two-Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201606388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Sungmin Kang
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Eun-Woo Lee
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Tianqi Li
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Xiaobin Liang
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Masatoshi Tokita
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Ken Nakajima
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Junji Watanabe
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
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14
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Kang S, Lee EW, Li T, Liang X, Tokita M, Nakajima K, Watanabe J. Two-Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules. Angew Chem Int Ed Engl 2016; 55:11552-6. [DOI: 10.1002/anie.201606388] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Sungmin Kang
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Eun-Woo Lee
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Tianqi Li
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Xiaobin Liang
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Masatoshi Tokita
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Ken Nakajima
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
| | - Junji Watanabe
- Department of Chemical Science and Engineering; School of Materials and Chemical Technology; Tokyo Institute of Technology; 2-12-1 O-okayama Tokyo 152-8552 Japan
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15
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Piot BA, Desrat W, Maude DK, Kazazis D, Cavanna A, Gennser U. Disorder-Induced Stabilization of the Quantum Hall Ferromagnet. PHYSICAL REVIEW LETTERS 2016; 116:106801. [PMID: 27015501 DOI: 10.1103/physrevlett.116.106801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Indexed: 06/05/2023]
Abstract
We report on an absolute measurement of the electronic spin polarization of the ν=1 integer quantum Hall state. The spin polarization is extracted in the vicinity of ν=1 (including at exactly ν=1) via resistive NMR experiments performed at different magnetic fields (electron densities) and Zeeman energy configurations. At the lowest magnetic fields, the polarization is found to be complete in a narrow region around ν=1. Increasing the magnetic field (electron density) induces a significant depolarization of the system, which we attribute to a transition between the quantum Hall ferromagnet and the Skyrmion glass phase theoretically expected as the ratio between Coulomb interactions and disorder is increased. These observations account for the fragility of the polarization previously observed in high mobility 2D electron gas and experimentally demonstrate the existence of an optimal amount of disorder to stabilize the ferromagnetic state.
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Affiliation(s)
- B A Piot
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL, F-38042 Grenoble, France
| | - W Desrat
- Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier, F-34095 Montpellier, France
| | - D K Maude
- Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL, F-31400 Toulouse, France
| | - D Kazazis
- CNRS, Laboratoire de Photonique et de Nanostructures (LPN), 91460 Marcoussis, France
| | - A Cavanna
- CNRS, Laboratoire de Photonique et de Nanostructures (LPN), 91460 Marcoussis, France
| | - U Gennser
- CNRS, Laboratoire de Photonique et de Nanostructures (LPN), 91460 Marcoussis, France
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16
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Cattaneo L, Kos Ž, Savoini M, Kouwer P, Rowan A, Ravnik M, Muševič I, Rasing T. Electric field generation of Skyrmion-like structures in a nematic liquid crystal. SOFT MATTER 2016; 12:853-8. [PMID: 26549212 PMCID: PMC5299589 DOI: 10.1039/c5sm01726b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 10/30/2015] [Indexed: 06/05/2023]
Abstract
Skyrmions are particle-like topological objects that are increasingly drawing attention in condensed matter physics, where they are connected to inversion symmetry breaking and chirality. Here we report the generation of stable Skyrmion-like structures in a thin nematic liquid crystal film on chemically patterned patchy surfaces. Using the interplay of material elasticity and surface boundary conditions, we use a strong electric field to quench the nematic liquid crystal from a fully aligned phase to vortex-like nematic liquid crystal structures, centered on patterned patches, which carry two different sorts of topological defects. Numerical calculations reveal that these are Skyrmion-like structures, seeded from the surface boojum topological defects and swirling towards the second confining surface. These observations, supported by numerical methods, demonstrate the possibility to generate, manipulate and study Skyrmion-like objects in nematic liquid crystals on patterned surfaces.
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Affiliation(s)
- Laura Cattaneo
- Radboud University, Institute of Molecules and Materials (IMM), Heyendaalseweg 135, 6525 AJ, Nijmegen, Netherlands
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17
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Generic Aspects of Skyrmion Lattices in Chiral Magnets. TOPOLOGICAL STRUCTURES IN FERROIC MATERIALS 2016. [DOI: 10.1007/978-3-319-25301-5_1] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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18
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Fractionally charged skyrmions in fractional quantum Hall effect. Nat Commun 2015; 6:8981. [PMID: 26608906 PMCID: PMC4674824 DOI: 10.1038/ncomms9981] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2015] [Accepted: 10/22/2015] [Indexed: 11/17/2022] Open
Abstract
The fractional quantum Hall effect has inspired searches for exotic emergent topological particles, such as fractionally charged excitations, composite fermions, abelian and nonabelian anyons and Majorana fermions. Fractionally charged skyrmions, which support both topological charge and topological vortex-like spin structure, have also been predicted to occur in the vicinity of 1/3 filling of the lowest Landau level. The fractional skyrmions, however, are anticipated to be exceedingly fragile, suppressed by very small Zeeman energies. Here we show that, slightly away from 1/3 filling, the smallest manifestations of the fractional skyrmion exist in the excitation spectrum for a broad range of Zeeman energies, and appear in resonant inelastic light scattering experiments as well-defined resonances slightly below the long wavelength spin wave mode. The spectroscopy of these exotic bound states serves as a sensitive tool for investigating the residual interaction between composite fermions, responsible for delicate new fractional quantum Hall states in this filling factor region. It is predicted that fractionally charged skyrmions, topologically protected vortex-like spin configurations, may exist in systems exhibiting fractional quantum Hall states. Here, the authors demonstrate the existence of such objects in GaAs single quantum wells.
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19
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Pusep YA, Tavares BGM, Tito MA, dos Santos LF, LaPierre RR. Magnetic field driven interminiband charge transfer in InGaAs/InP superlattices. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:245601. [PMID: 26000711 DOI: 10.1088/0953-8984/27/24/245601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The characteristic energies, occupancies and polarizations of the minibands formed by the Γ-Γ and Γ-Xz interlayer electon tunnelings in the InGaAs/InP superlattices are studied in the regime of the integer quantum Hall effect by polarization resolved photoluminescence. Accordingly, the magnetic field induced shrinkage of the interminiband gap, predicted by the theory, and as a consequence, the redistribution of charge over the superlattice minibands and the depolarization of the quantum Hall electron states are observed at odd filling factors. The response of the electrons residing in the InGaAs/InP superlattice minibands to the magnetic field is found very similar to the corresponding response of the electrons confined in the symmetric and anti-symmetric two-dimensional minibands of GaAs/AlGaAs double quantum wells. The presented results are evidence of the formation of the correlated states in multi-component electron systems formed in semiconductor multiple layers at odd filling factors.
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Affiliation(s)
- Yu A Pusep
- Instituto de Fisica de São Carlos, Universidade de São Paulo, 13560-970 Sao Carlos, SP, Brazil
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20
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Fukuda JI. Stability of cholesteric blue phases in the presence of a guest component. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:041704. [PMID: 23214600 DOI: 10.1103/physreve.86.041704] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Indexed: 06/01/2023]
Abstract
We investigate theoretically, with the aid of numerical calculations based on a Landau-de Gennes theory, how two cubic cholesteric blue phases of a chiral liquid crystal, BP I and BP II, are stabilized when a guest component, such as a polymer network, is introduced and replace energetically costly defect regions. We show that the temperature range of stable BP I is significantly widened by the guest component, while the stability of BP II is only modestly enhanced.
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Affiliation(s)
- Jun-ichi Fukuda
- Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568, Japan.
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21
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Romers JC, Schoutens K. Spin texture readout of a moore-read topological quantum register. PHYSICAL REVIEW LETTERS 2012; 109:126802. [PMID: 23005972 DOI: 10.1103/physrevlett.109.126802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Indexed: 06/01/2023]
Abstract
We study the composite charged spin texture (CST) over the Moore-Read quantum Hall state that arises when a collection of elementary CSTs is moved to the same location. Following an algebraic approach based on the characteristic pair correlations of the Moore-Read state, we find that the spin texture associated with a composite CST is set by the fusion sector of the underlying non-Abelian quasiparticles. This phenomenon provides a novel way to read out the quantum register of a non-Abelian topologically ordered phase.
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Affiliation(s)
- J C Romers
- Institute for Theoretical Physics, University of Amsterdam, The Netherlands.
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22
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Fukuda JI. Stabilization of blue phases by the variation of elastic constants. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:020701. [PMID: 22463144 DOI: 10.1103/physreve.85.020701] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Indexed: 05/31/2023]
Abstract
We study theoretically the effect of the variation of the elastic constants on the stability of cholesteric blue phases (BPs). We demonstrate that the stability of BPs is greatly enhanced when the bend elastic constant K(33) is smaller, in agreement with recent experimental findings. Larger splay (K(11)) and twist (K(22)) elastic constants also stabilize BPs. Our argument sheds light on the subtle effect of the variation of the elastic constants on the stability of BPs, and could guide the synthesis of liquid crystals with a wider temperature range of stable BPs.
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Affiliation(s)
- Jun-ichi Fukuda
- Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568, Japan.
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23
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Choi JY, Kwon WJ, Shin YI. Observation of topologically stable 2D Skyrmions in an antiferromagnetic spinor Bose-Einstein condensate. PHYSICAL REVIEW LETTERS 2012; 108:035301. [PMID: 22400755 DOI: 10.1103/physrevlett.108.035301] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2011] [Indexed: 05/31/2023]
Abstract
We present the creation and time evolution of two-dimensional Skyrmion excitations in an antiferromagnetic spinor Bose-Einstein condensate. Using a spin rotation method, the Skyrmion spin textures were imprinted on a sodium condensate in a polar phase, where the two-dimensional Skyrmion is topologically protected. The Skyrmion was observed to be stable on a short time scale of a few tens of ms but to dynamically deform its shape and eventually decay to a uniform spin texture. The deformed spin textures reveal that the decay dynamics involves breaking the polar phase inside the condensate without having topological charge density flow through the boundary of the finite-sized sample. We discuss the possible formation of half-quantum vortices in the deformation process.
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Affiliation(s)
- Jae-yoon Choi
- Center for Subwavelength Optics and Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
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24
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Kobayashi T, Kumada N, Ota T, Sasaki S, Hirayama Y. Low-frequency spin fluctuations in Skyrmions confined by wires: measurements of local nuclear spin relaxation. PHYSICAL REVIEW LETTERS 2011; 107:126807. [PMID: 22026789 DOI: 10.1103/physrevlett.107.126807] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2011] [Indexed: 05/31/2023]
Abstract
We investigate low-frequency electron spin dynamics in a quantum Hall system with wire confinement by nuclear spin relaxation measurements. We developed a technique to measure the local nuclear spin relaxation rate T(1)(-1). T(1)(-1) is enhanced on both sides of the local filling factor ν(wire)=1, reflecting low-frequency fluctuations of electron spins associated with Skyrmions inside the wire. As the wire width is decreased, the fast nuclear spin relaxation is suppressed in a certain range of Skyrmion density. This suggests that the multi-Skyrmion state is modified and the low-frequency spin fluctuations are suppressed by the wire confinement.
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Affiliation(s)
- Takashi Kobayashi
- NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198, Japan
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25
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Raičević I, Popović D, Panagopoulos C, Benfatto L, Silva Neto MB, Choi ES, Sasagawa T. Skyrmions in a doped antiferromagnet. PHYSICAL REVIEW LETTERS 2011; 106:227206. [PMID: 21702631 DOI: 10.1103/physrevlett.106.227206] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Indexed: 05/31/2023]
Abstract
Magnetization and magnetoresistance have been measured in insulating antiferromagnetic La2Cu0.97Li0.03O4 over a wide range of temperatures, magnetic fields, and field orientations. The magnetoresistance step associated with a weak ferromagnetic transition exhibits a striking nonmonotonic temperature dependence, consistent with the presence of Skyrmions.
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Affiliation(s)
- I Raičević
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
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26
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Pan W, Reno JL, Li D, Brueck SRJ. Quantum Hall ferromagnetism in the presence of tunable disorder. PHYSICAL REVIEW LETTERS 2011; 106:156806. [PMID: 21568597 DOI: 10.1103/physrevlett.106.156806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2010] [Indexed: 05/30/2023]
Abstract
In this Letter, we report our recent experimental results on the energy gap of the ν=1 quantum Hall state (Δ(ν=1)) in a quantum antidot array sample, where the effective disorder potential can be tuned continuously. Δ(ν=1) is nearly constant at small effective disorders, and collapses at a critical disorder. Moreover, in the weak disorder regime, Δ(ν=1) shows a B(total)(1/2) dependence in tilted magnetic field measurements, while in the strong disorder regime, Δ(ν=1) is linear in B(total), where B(total) is the total magnetic field at ν=1. We discuss our results within several models involving the quantum Hall ferromagnetic ground state and its interplay with sample disorder.
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Affiliation(s)
- W Pan
- Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA
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27
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Quasi-two-dimensional Skyrmion lattices in a chiral nematic liquid crystal. Nat Commun 2011; 2:246. [DOI: 10.1038/ncomms1250] [Citation(s) in RCA: 164] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Accepted: 02/22/2011] [Indexed: 11/08/2022] Open
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28
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Yeoh LA, Srinivasan A, Martin TP, Klochan O, Micolich AP, Hamilton AR. Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2010; 81:113905. [PMID: 21133484 DOI: 10.1063/1.3502645] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We report the design and development of a piezoelectric sample rotation system, and its integration into an Oxford Instruments Kelvinox 100 dilution refrigerator, for orientation-dependent studies of quantum transport in semiconductor nanodevices at millikelvin temperatures in magnetic fields up to 10 T. Our apparatus allows for continuous in situ rotation of a device through >100° in two possible configurations. The first enables rotation of the field within the plane of the device, and the second allows the field to be rotated from in-plane to perpendicular to the device plane. An integrated angle sensor coupled with a closed-loop feedback system allows the device orientation to be known to within ±0.03° while maintaining the sample temperature below 100 mK.
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Affiliation(s)
- L A Yeoh
- School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
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29
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Zhu H, Chen YP, Jiang P, Engel LW, Tsui DC, Pfeiffer LN, West KW. Observation of a pinning mode in a Wigner solid with ν=1/3 fractional quantum Hall excitations. PHYSICAL REVIEW LETTERS 2010; 105:126803. [PMID: 20867666 DOI: 10.1103/physrevlett.105.126803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Indexed: 05/29/2023]
Abstract
We report the observation of a resonance in the microwave spectra of the real diagonal conductivities of a two-dimensional electron system within a range of ∼ ± 0.015 from filling factor ν = 1/3. The resonance is remarkably similar to resonances previously observed near integer ν, and is interpreted as the collective pinning mode of a disorder-pinned Wigner solid phase of e/3-charged carriers.
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Affiliation(s)
- Han Zhu
- Princeton University, Princeton, New Jersey 08544, USA
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30
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Zhu H, Sambandamurthy G, Chen YP, Jiang P, Engel LW, Tsui DC, Pfeiffer LN, West KW. Pinning-mode resonance of a Skyrme crystal near Landau-level filling factor ν=1. PHYSICAL REVIEW LETTERS 2010; 104:226801. [PMID: 20867191 DOI: 10.1103/physrevlett.104.226801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Indexed: 05/29/2023]
Abstract
Microwave pinning-mode resonances found around integer quantum Hall effects, are a signature of crystallized quasiparticles or holes. Application of in-plane magnetic field to these crystals, increasing the Zeeman energy, has negligible effect on the resonances just below Landau-level filling ν=2, but increases the pinning frequencies near ν=1, particularly for smaller quasiparticle or hole densities. The charge dynamics near ν=1, characteristic of a crystal order, are affected by spin, in a manner consistent with a Skyrme crystal.
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Affiliation(s)
- Han Zhu
- Princeton University, Princeton, New Jersey 08544, USA
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31
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Dial OE, Ashoori RC, Pfeiffer LN, West KW. Anomalous structure in the single particle spectrum of the fractional quantum Hall effect. Nature 2010; 464:566-70. [DOI: 10.1038/nature08941] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Accepted: 02/18/2010] [Indexed: 11/09/2022]
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32
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Padmanabhan M, Gokmen T, Shayegan M. Ferromagnetic fractional quantum Hall states in a valley-degenerate two-dimensional electron system. PHYSICAL REVIEW LETTERS 2010; 104:016805. [PMID: 20366382 DOI: 10.1103/physrevlett.104.016805] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Indexed: 05/29/2023]
Abstract
We study a two-dimensional electron system where the electrons occupy two conduction band valleys with anisotropic Fermi contours and strain-tunable occupation. We observe persistent quantum Hall states at filling factors nu=1/3 and 5/3 even at zero strain when the two valleys are degenerate. This is reminiscent of the quantum Hall ferromagnet formed at nu=1 in the same system at zero strain. In the absence of a theory for a system with anisotropic valleys, we compare the energy gaps measured at nu=1/3 and 5/3 to the available theory developed for single-valley, two-spin systems, and find that the gaps and their rates of rise with strain are much smaller than predicted.
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Affiliation(s)
- Medini Padmanabhan
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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33
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Murthy G. Hamiltonian theory of disorder at nu = 1/3. PHYSICAL REVIEW LETTERS 2009; 103:206802. [PMID: 20365998 DOI: 10.1103/physrevlett.103.206802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Indexed: 05/29/2023]
Abstract
The Hamiltonian theory of the fractional quantum Hall regime provides a simple and tractable approach to calculating gaps, polarizations, and many other physical quantities. In this Letter we include disorder in our treatment and show that a simple model with minimal assumptions produces results consistent with a range of experiments. In particular, the interplay between disorder and interactions can result in experimental signatures which mimic those of spin textures.
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Affiliation(s)
- Ganpathy Murthy
- Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
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34
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Plochocka P, Schneider JM, Maude DK, Potemski M, Rappaport M, Umansky V, Bar-Joseph I, Groshaus JG, Gallais Y, Pinczuk A. Optical absorption to probe the quantum Hall ferromagnet at filling factor nu=1. PHYSICAL REVIEW LETTERS 2009; 102:126806. [PMID: 19392309 DOI: 10.1103/physrevlett.102.126806] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Indexed: 05/27/2023]
Abstract
Optical absorption measurements are used to probe the spin polarization in the integer and fractional quantum Hall effect regimes. The system is fully spin polarized only at filling factor nu=1 and at very low temperatures ( approximately 40 mK). A small change in filling factor (deltanu approximately +/-0.01) leads to a significant depolarization. This suggests that the itinerant quantum Hall ferromagnet at nu=1 is surprisingly fragile against increasing temperature, or against small changes in filling factor.
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Affiliation(s)
- P Plochocka
- Laboratoire National des Champs Magnétiques Intenses, Grenoble High Magnetic Field Laboratory, 38042 Grenoble, France.
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35
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Dean CR, Piot BA, Hayden P, Das Sarma S, Gervais G, Pfeiffer LN, West KW. Contrasting behavior of the 5/2 and 7/3 fractional quantum Hall effect in a tilted field. PHYSICAL REVIEW LETTERS 2008; 101:186806. [PMID: 18999851 DOI: 10.1103/physrevlett.101.186806] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Indexed: 05/27/2023]
Abstract
Using a tilted-field geometry, the effect of an in-plane magnetic field on the even denominator nu=5/2 fractional quantum Hall state is studied. The energy gap of the nu=5/2 state is found to collapse linearly with the in-plane magnetic field above approximately 0.5 T. In contrast, a strong enhancement of the gap is observed for the nu=7/3 state. The radically distinct tilted-field behavior between the two states is discussed in terms of Zeeman and magneto-orbital coupling within the context of the proposed Moore-Read Pfaffian wave function for the 5/2 fractional quantum Hall effect.
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Affiliation(s)
- C R Dean
- Department of Physics, McGill University, Montreal, H3A 2T8, Canada
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36
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Dutta SB, Shankar R. Bosonization, coherent states and semiclassical quantum Hall skyrmions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:275237. [PMID: 21694398 DOI: 10.1088/0953-8984/20/27/275237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We bosonize (2+1)-dimensional fermionic theory using coherent states. The gauge-invariant subspace of boson-Chern-Simons Hilbert space is mapped to fermionic Hilbert space. This subspace is then equipped with a coherent state basis. These coherent states are labelled by a dynamic spinor field. The label manifold could be assigned a physical meaning in terms of density and spin density. A path-integral representation of the evolution operator in terms of these physical variables is given. The corresponding classical theory when restricted to LLL is described by spin fluctuations alone and is found to be the NLSM with Hopf term. The formalism developed here is suitable to study quantum Hall skyrmions semiclassically and/or beyond the hydrodynamic limit. The effects of Landau level mixing or the presence of slowly varying external fields can also be easily incorporated.
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Affiliation(s)
- Sreedhar B Dutta
- Korea Institute for Advanced Study, 87 Hoegiro, Dongdaemun-gu, Seoul 130-722, Korea
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37
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Gallais Y, Yan J, Pinczuk A, Pfeiffer LN, West KW. Soft spin wave near nu=1: evidence for a magnetic instability in Skyrmion systems. PHYSICAL REVIEW LETTERS 2008; 100:086806. [PMID: 18352652 DOI: 10.1103/physrevlett.100.086806] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Indexed: 05/26/2023]
Abstract
The ground state of the two-dimensional electron gas near nu=1 is investigated by inelastic light scattering measurements carried down to very low temperatures. Away from nu=1, the ferromagnetic spin wave collapses and a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave shows soft behavior as its energy increases with temperature and reaches the Zeeman energy for temperatures above 2 K. The observed softening indicates an instability of the two-dimensional electron gas towards a magnetic order that breaks spin rotational symmetry. We discuss our findings in light of the possible existence of a Skyrme crystal.
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Affiliation(s)
- Yann Gallais
- Departments of Physics and of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
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38
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Groshaus JG, Dujovne I, Gallais Y, Hirjibehedin CF, Pinczuk A, Tan YW, Stormer H, Dennis BS, Pfeiffer LN, West KW. Spin texture and magnetoroton excitations at nu=1/3. PHYSICAL REVIEW LETTERS 2008; 100:046804. [PMID: 18352317 DOI: 10.1103/physrevlett.100.046804] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2007] [Indexed: 05/26/2023]
Abstract
Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3.
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Affiliation(s)
- Javier G Groshaus
- Physics & Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
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39
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Dial OE, Ashoori RC, Pfeiffer LN, West KW. High-resolution spectroscopy of two-dimensional electron systems. Nature 2007; 448:176-9. [PMID: 17625561 DOI: 10.1038/nature05982] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2006] [Accepted: 01/04/2007] [Indexed: 11/09/2022]
Abstract
Spectroscopic methods involving the sudden injection or ejection of electrons in materials are a powerful probe of electronic structure and interactions. These techniques, such as photoemission and tunnelling, yield measurements of the 'single-particle' density of states spectrum of a system. This density of states is proportional to the probability of successfully injecting or ejecting an electron in these experiments. It is equal to the number of electronic states in the system able to accept an injected electron as a function of its energy, and is among the most fundamental and directly calculable quantities in theories of highly interacting systems. However, the two-dimensional electron system (2DES), host to remarkable correlated electron states such as the fractional quantum Hall effect, has proved difficult to probe spectroscopically. Here we present an improved version of time-domain capacitance spectroscopy that allows us to measure the single-particle density of states of a 2DES with unprecedented fidelity and resolution. Using the method, we perform measurements of a cold 2DES, providing direct measurements of interesting correlated electronic effects at energies that are difficult to reach with other techniques; these effects include the single-particle exchange-enhanced spin gap, single-particle lifetimes in the quantum Hall system, and exchange splitting of Landau levels not at the Fermi surface.
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Affiliation(s)
- O E Dial
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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40
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Van'kov AB, Kulik LV, Kukushkin IV, Kirpichev VE, Dickmann S, Zhilin VM, Smet JH, von Klitzing K, Wegscheider W. Low-magnetic-field divergence of the electronic g factor obtained from the cyclotron spin-flip mode of the nu=1 quantum Hall ferromagnet. PHYSICAL REVIEW LETTERS 2006; 97:246801. [PMID: 17280306 DOI: 10.1103/physrevlett.97.246801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Indexed: 05/13/2023]
Abstract
We report an inelastic light scattering study of the cyclotron spin-flip mode in the two-dimensional electron system at filling nu=1. The energy of this mode can serve as a probe of the many-body exchange interaction on short length scales. Its magnetic field dependence is compared with predictions based on Hartree-Fock theory. They agree well when including the nonzero width of the electron system. From the measured energies, the exchange enhanced g factor is extracted. It diverges at small fields and differs largely from g factors obtained via transport activation studies.
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Affiliation(s)
- A B Van'kov
- Institute for Solid State Physics, Russian Academy of Sciences, Chernogolovka 142432, Russia
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41
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Bowers CR, Caldwell JD, Gusev G, Kovalev AE, Olshanetsky E, Reno JL, Simmons JA, Vitkalov SA. Dynamic nuclear polarization and nuclear magnetic resonance in the vicinity of edge states of a 2DES in GaAs quantum wells. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2006; 29:52-65. [PMID: 16216476 DOI: 10.1016/j.ssnmr.2005.08.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2005] [Revised: 08/23/2005] [Indexed: 05/04/2023]
Abstract
Nuclear magnetic resonance is detected via the in-plane conductivity of a two-dimensional electron system at unity Landau level filling factor in the regime of the quantum Hall effect in narrow and wide quantum wells. The NMR is spatially selective to nuclei with a coupling to electrons in the current carrying edge states at the perimeter of the 2DES. Interpretation of the electron-nuclear double resonance signals is facilitated by numerical simulations. A new RF swept method for conductivity-detected NMR is introduced which offers more efficient signal averaging. The method is applied to the study of electric quadrupole interactions, weakly allowed overtone transitions, and evaluation of the extent of electron wave function delocalization in the wide quantum well.
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Affiliation(s)
- Clifford R Bowers
- Department of Chemistry, National High Magnetic Field Laboratory, University of Florida, Gainesville, Florida 32611-7200, USA.
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42
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Shkolnikov YP, Misra S, Bishop NC, De Poortere EP, Shayegan M. Observation of quantum Hall "valley Skyrmions". PHYSICAL REVIEW LETTERS 2005; 95:066809. [PMID: 16090979 DOI: 10.1103/physrevlett.95.066809] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2005] [Indexed: 05/03/2023]
Abstract
We report measurements of the interaction-induced quantum Hall effect in a spin-polarized AlAs two-dimensional electron system where the electrons occupy two in-plane conduction band valleys. Via the application of in-plane strain, we tune the energies of these valleys and measure the energy gap of the quantum Hall state at filling factor nu = 1. The gap has a finite value even at zero strain and, with strain, rises much faster than expected from a single-particle picture, suggesting that the lowest energy charged excitations at nu = 1 are "valley Skyrmions."
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Affiliation(s)
- Y P Shkolnikov
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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43
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Gervais G, Stormer HL, Tsui DC, Kuhns PL, Moulton WG, Reyes AP, Pfeiffer LN, Baldwin KW, West KW. Evidence for skyrmion crystallization from NMR relaxation experiments. PHYSICAL REVIEW LETTERS 2005; 94:196803. [PMID: 16090197 DOI: 10.1103/physrevlett.94.196803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2004] [Indexed: 05/03/2023]
Abstract
A resistively detected NMR technique was used to probe the two-dimensional electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate (1/T(1)) was extracted at near complete filling of the first Landau level by electrons. The nuclear spin of (75)As is found to relax much more efficiently with T --> 0 and when a well developed quantum Hall state with R(xx) approximately 0 occurs. The data show a remarkable correlation between the nuclear spin relaxation and localization. This suggests that the magnetic ground state near complete filling of the first Landau level may contain a lattice of topological spin texture, i.e., a Skyrmion crystal.
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Affiliation(s)
- G Gervais
- Department of Physics, Columbia University, New York, New York 10027 USA
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44
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Groshaus JG, Umansky V, Shtrikman H, Levinson Y, Bar-Joseph I. Absorption spectrum around nu=1: evidence for a small-size Skyrmion. PHYSICAL REVIEW LETTERS 2004; 93:096802. [PMID: 15447123 DOI: 10.1103/physrevlett.93.096802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2004] [Indexed: 05/24/2023]
Abstract
We measure the absorption spectrum of a two-dimensional electron system (2DES) in a GaAs quantum well in the presence of a perpendicular magnetic field. We focus on the absorption spectrum into the lowest Landau level around nu=1. We find that the spectrum consists of bound electron-hole complexes, trionlike and excitonlike. We show that their oscillator strength is a powerful probe of the 2DES spatial correlations. We find that near nu=1 the 2DES ground state consists of Skyrmions of small size (a few magnetic lengths).
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Affiliation(s)
- J G Groshaus
- Department of Condensed Matter Physics, The Weizmann Institute of Science, Rehovot, Israel.
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45
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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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46
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Khandelwal P, Dementyev AE, Kuzma NN, Barrett SE, Pfeiffer LN, West KW. Spectroscopic evidence for the localization of Skyrmions near nu = 1 as T --> 0. PHYSICAL REVIEW LETTERS 2001; 86:5353-5356. [PMID: 11384496 DOI: 10.1103/physrevlett.86.5353] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2000] [Indexed: 05/23/2023]
Abstract
Optically pumped nuclear magnetic resonance measurements of 71Ga spectra were carried out in an n-doped GaAs/Al(0.1)Ga0.9As multiple quantum well sample near the integer quantum Hall ground state nu = 1. As the temperature is lowered (down to T approximately 0.3 K), a "tilted plateau" emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional Skyrmions.
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Affiliation(s)
- P Khandelwal
- Department of Physics, Yale University, New Haven, Connecticut 06511, USA
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47
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Ino K. Field theory of spin-singlet quantum Hall states. PHYSICAL REVIEW LETTERS 2001; 86:882-885. [PMID: 11177964 DOI: 10.1103/physrevlett.86.882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2000] [Indexed: 05/23/2023]
Abstract
We formulate a field theory for the Haldane-Rezayi quantum Hall state and its variants. A new essential ingredient is a class of super Chern-Simons field.
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Affiliation(s)
- K Ino
- Nomura Research Institute, Hongo 2-2-9, Bunkyo-ku, Tokyo, 113-0033, Japan
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48
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Spielman IB, Eisenstein JP, Pfeiffer LN, West KW. Resonantly enhanced tunneling in a double layer quantum hall ferromagnet. PHYSICAL REVIEW LETTERS 2000; 84:5808-5811. [PMID: 10991060 DOI: 10.1103/physrevlett.84.5808] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2000] [Indexed: 05/23/2023]
Abstract
The tunneling conductance between two parallel 2D electron systems has been measured in a regime of strong interlayer Coulomb correlations. At total Landau level filling nuT=1 the tunnel spectrum changes qualitatively when the boundary separating the compressible phase from the ferromagnetic quantized Hall state is crossed. A huge resonant enhancement replaces the strongly suppressed equilibrium tunneling characteristic of weakly coupled layers. The possible relationship of this enhancement to the Goldstone mode of the broken symmetry ground state is discussed.
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Affiliation(s)
- I B Spielman
- California Institute of Technology, Pasadena, California 91125, USA
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49
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Moon K, Mullen K. Thermodynamic phase diagram of the quantum hall skyrmion system. PHYSICAL REVIEW LETTERS 2000; 84:975-978. [PMID: 11017419 DOI: 10.1103/physrevlett.84.975] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/1999] [Indexed: 05/23/2023]
Abstract
We numerically study the interacting quantum Hall Skyrmion system based on the Chern-Simons action. By noticing that the action is invariant under global spin rotations in the spin space with respect to the magnetic field direction, we obtain the low-energy effective action for a many-Skyrmion system. Performing extensive molecular dynamics simulations, we establish the thermodynamic phase diagram for a many-Skyrmion system.
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Affiliation(s)
- K Moon
- Department of Physics, Yonsei University, Seoul 120-749, Korea
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50
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Fal'ko VI, Iordanskii SV. Spin-orbit coupling effect on quantum hall ferromagnets with vanishing zeeman energy. PHYSICAL REVIEW LETTERS 2000; 84:127-130. [PMID: 11015851 DOI: 10.1103/physrevlett.84.127] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/1999] [Indexed: 05/23/2023]
Abstract
We present the phase diagram of a ferromagnetic nu = 2N+1 quantum Hall liquid in a narrow quantum well with vanishing single-particle Zeeman splitting, varepsilon(Z), and a pronounced spin-orbit coupling. Upon decreasing varepsilon(Z) the spin-polarization field of a liquid takes, first, the easy-axis configuration, followed by the formation of a helical state which affects the transport and NMR properties of a liquid and the form of topological defects in it.
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Affiliation(s)
- VI Fal'ko
- School of Physics and Chemistry, Lancaster University, LA1 4YB, United Kingdom
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