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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Zhang L, Hu Y, Yao Z, Liu X, Luo W, Sun K, Chakraborty T. Controllable quantum scars induced by spin-orbit couplings in quantum dots. DISCOVER NANO 2024; 19:72. [PMID: 38684632 PMCID: PMC11058183 DOI: 10.1186/s11671-024-04015-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 04/16/2024] [Indexed: 05/02/2024]
Abstract
Spin-orbit couplings (SOCs), originating from the relativistic corrections in the Dirac equation, offer nonlinearity in the classical limit and are capable of driving chaotic dynamics. In a nanoscale quantum dot confined by a two-dimensional parabolic potential with SOCs, various quantum scar states emerge quasi-periodically in the eigenstates of the system, when the ratio of confinement energies in the two directions is nearly commensurable. The scars, displaying both quantum interference and classical trajectory features on the electron density, due to relativistic effects, serve as a bridge between the classical and quantum behaviors of the system. When the strengths of Rashba and Dresselhaus SOCs are identical, the chaos in the classical limit is eliminated as the classical Hamilton's equations become linear, leading to the disappearance of all quantum scar states. Importantly, the quantum scars induced by SOCs are robust against small perturbations of system parameters. With precise control achievable through external gating, the quantum scar induced by Rashba SOC is fully controllable and detectable.
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Affiliation(s)
- Lin Zhang
- School of Physics, Central South University, Changsha, 410083, China
| | - Yutao Hu
- School of Physics, Central South University, Changsha, 410083, China
| | - Zhao Yao
- School of Physics, Central South University, Changsha, 410083, China
| | - Xiaochi Liu
- School of Physics, Central South University, Changsha, 410083, China
| | - Wenchen Luo
- School of Physics, Central South University, Changsha, 410083, China.
| | - Kehui Sun
- School of Physics, Central South University, Changsha, 410083, China
| | - Tapash Chakraborty
- Department of Physics and Astronomy, University of Manitoba, Winnipeg, R3T 2N2, Canada
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3
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Yoo HM, Korkusinski M, Miravet D, Baldwin KW, West K, Pfeiffer L, Hawrylak P, Ashoori RC. Time, momentum, and energy resolved pump-probe tunneling spectroscopy of two-dimensional electron systems. Nat Commun 2023; 14:7440. [PMID: 37978193 PMCID: PMC10656415 DOI: 10.1038/s41467-023-43268-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 11/06/2023] [Indexed: 11/19/2023] Open
Abstract
Real-time probing of electrons can uncover intricate relaxation mechanisms and many-body interactions in strongly correlated materials. Here, we introduce time, momentum, and energy resolved pump-probe tunneling spectroscopy (Tr-MERTS). The method allows the injection of electrons at a particular energy and observation of their subsequent decay in energy-momentum space. Using Tr-MERTS, we visualize electronic decay processes, with lifetimes from tens of nanoseconds to tens of microseconds, in Landau levels formed in a GaAs quantum well. Although most observed features agree with simple energy-relaxation, we discovered a splitting in the nonequilibrium energy spectrum in the vicinity of a ferromagnetic state. An exact diagonalization study suggests that the splitting arises from a maximally spin-polarized state with higher energy than a conventional equilibrium skyrmion. Furthermore, we observe time-dependent relaxation of the splitting, which we attribute to single-flipped spins forming skyrmions. These results establish Tr-MERTS as a powerful tool for studying the properties of a 2DES beyond equilibrium.
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Affiliation(s)
- H M Yoo
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - M Korkusinski
- Emerging Technologies Division, National Research Council of Canada, Ottawa, ON, K1A 0R6, Canada
| | - D Miravet
- Department of Physics, University of Ottawa, Ottawa, ON, K1N 6N5, Canada
| | - K W Baldwin
- Department of Electrical Engineering, Princeton University, Princeton, NJ, 08544, USA
| | - K West
- Department of Electrical Engineering, Princeton University, Princeton, NJ, 08544, USA
| | - L Pfeiffer
- Department of Electrical Engineering, Princeton University, Princeton, NJ, 08544, USA
| | - P Hawrylak
- Department of Physics, University of Ottawa, Ottawa, ON, K1N 6N5, Canada
| | - R C Ashoori
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
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4
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Millington-Hotze P, Manna S, Covre da Silva SF, Rastelli A, Chekhovich EA. Nuclear spin diffusion in the central spin system of a GaAs/AlGaAs quantum dot. Nat Commun 2023; 14:2677. [PMID: 37160864 PMCID: PMC10170165 DOI: 10.1038/s41467-023-38349-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Accepted: 04/24/2023] [Indexed: 05/11/2023] Open
Abstract
The spin diffusion concept provides a classical description of a purely quantum-mechanical evolution in inhomogeneously polarized many-body systems such as nuclear spin lattices. The central spin of a localized electron alters nuclear spin diffusion in a way that is still poorly understood. Here, spin diffusion in a single GaAs/AlGaAs quantum dot is witnessed in the most direct manner from oscillatory spin relaxation dynamics. Electron spin is found to accelerate nuclear spin relaxation, from which we conclude that the long-discussed concept of a Knight-field-gradient diffusion barrier does not apply to GaAs epitaxial quantum dots. Our experiments distinguish between non-diffusion relaxation and spin diffusion, allowing us to conclude that diffusion is accelerated by the central electron spin. Such acceleration is observed up to unexpectedly high magnetic fields - we propose electron spin-flip fluctuations as an explanation. Diffusion-limited nuclear spin lifetimes range between 1 and 10 s, which is sufficiently long for quantum information storage and processing.
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Affiliation(s)
- Peter Millington-Hotze
- Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, United Kingdom
| | - Santanu Manna
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenberger Str. 69, Linz, 4040, Austria
- Department of Electrical Engineering, Indian Institute of Technology Delhi, New Delhi, 110016, India
| | - Saimon F Covre da Silva
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenberger Str. 69, Linz, 4040, Austria
| | - Armando Rastelli
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenberger Str. 69, Linz, 4040, Austria
| | - Evgeny A Chekhovich
- Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, United Kingdom.
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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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Li ZY, Zhang DQ, Lin SZ, Góźdź WT, Li B. Spontaneous organization and phase separation of skyrmions in chiral active matter. SOFT MATTER 2022; 18:7348-7359. [PMID: 36124977 DOI: 10.1039/d2sm00819j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Skyrmions are topologically protected vortex-like excitations that hold promise for applications such as information processing and electron manipulation. Here we combine theoretical analysis and numerical simulations to show that skyrmions can spontaneously emerge in chiral active matter without external confinements or regulation. Strikingly, these activity-driven skyrmions can either self-organize into a periodic, stable square lattice consisting of half Néel skyrmions and antiskyrmions, where the in-plane flows display an antiferromagnetic vortex array, or undergo phase separation between skyrmions with different topological numbers. We identify that the emerging skyrmion dynamics stems from the competition between the chiral and polar coherence length scales dictated by the interplay of intrinsic chirality, polarity, and elasticity in the system. Our results reveal unanticipated topological excitations, self-organization, and phase separation in non-equilibrium systems and also suggest a potential way towards engineering complicated bespoke skyrmionic structures through manipulating active matter.
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Affiliation(s)
- Zhong-Yi Li
- Institute of Biomechanics and Medical Engineering, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
| | - De-Qing Zhang
- Institute of Biomechanics and Medical Engineering, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
| | - Shao-Zhen Lin
- Aix Marseille Université, CNRS, Centre de Physique Théorique, Turing Center for Living Systems, 13009 Marseille, France
| | - Wojciech T Góźdź
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
| | - Bo Li
- Institute of Biomechanics and Medical Engineering, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
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7
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Morgenstern M, Goerbig M. Many-particle electron states in graphene. Science 2022; 375:263-264. [PMID: 35050651 DOI: 10.1126/science.abn2049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Markus Morgenstern
- II. Institute of Physics B and JARA-FIT, RWTH-Aachen University, 52074 Aachen, Germany
| | - Mark Goerbig
- Laboratoire de Physique des Solides, CNRS, Université Paris Saclay, Bât. 510, 91405 Orsay cedex, France
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8
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Tominaga Y, Takeda K. An electro-mechano-optical NMR probe for 1H– 13C double resonance in a superconducting magnet. Analyst 2022; 147:1847-1852. [DOI: 10.1039/d2an00220e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A compact nanomembrane radiofrequency-to-light transducer brings the emerging Electro-Mechano-Optical (EMO) NMR technique into the realm of practical NMR in chemistry using a superconducting magnet.
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Affiliation(s)
- Yusuke Tominaga
- Division of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan
| | - Kazuyuki Takeda
- Division of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan
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9
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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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10
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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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11
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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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12
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Guo C, Xiao M, Guo Y, Yuan L, Fan S. Meron Spin Textures in Momentum Space. PHYSICAL REVIEW LETTERS 2020; 124:106103. [PMID: 32216415 DOI: 10.1103/physrevlett.124.106103] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Accepted: 02/05/2020] [Indexed: 06/10/2023]
Abstract
We show that a momentum-space meron spin texture for electromagnetic fields in free space can be generated by controlling the interaction of light with a photonic crystal slab having a nonzero Berry curvature. These spin textures in momentum space have not been previously noted either in electronic or photonic systems. Breaking the inversion symmetry of a honeycomb photonic crystal gaps out the Dirac cones at the corners of Brillouin zone. The pseudospin textures of photonic bands near the gaps exhibit a meron or antimeron. Unlike the electronic systems, the pseudospin texture of the photonic modes manifests directly in the spin (polarization) texture of the leakage radiation, as the Dirac points can be above the light line. Such a spin texture provides a direct approach to visualize the local Berry curvature. Our work highlights the significant opportunities of using photonic structures for the exploration of topological spin textures, with potential applications towards topologically robust ways to manipulate polarizations and other modal characteristics of light.
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Affiliation(s)
- Cheng Guo
- Department of Applied Physics, Stanford University, Stanford, California 94305, USA
| | - Meng Xiao
- Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Yu Guo
- Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA
| | - Luqi Yuan
- Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA
- School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Shanhui Fan
- Ginzton Laboratory and Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA
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13
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Larionov AV, Stepanets-Khussein E, Kulik LV, Umansky V, Kukushkin IV. Investigation of spin stiffness in spin-depolarized states of two-dimensional electron systems with time-resolved Kerr rotation. Sci Rep 2020; 10:2270. [PMID: 32041986 PMCID: PMC7010672 DOI: 10.1038/s41598-020-58658-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 01/14/2020] [Indexed: 11/27/2022] Open
Abstract
An experimental technique based on time-resolved Kerr rotation allows a comparison of the spin stiffnesses of different spin-polarized and depolarized states in a two-dimensional electron system. With this technique, a new spin-correlated phase that has no known analogues was discovered. The new spin-depolarized phase is characterized by high spin stiffness equal to that of a spin-polarized quantum Hall ferromagnet.
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Affiliation(s)
- A V Larionov
- Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Russia.
| | - E Stepanets-Khussein
- Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Russia.,National Research University Higher School of Economics, 101000, Moscow, Russia
| | - L V Kulik
- Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Russia.,National Research University Higher School of Economics, 101000, Moscow, Russia
| | - V Umansky
- Braun Center for Submicron Research, Weizmann Institute of Science, Rehovot, 76100, Israel
| | - I V Kukushkin
- Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Russia.,National Research University Higher School of Economics, 101000, Moscow, Russia
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14
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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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15
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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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16
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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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17
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Luo W, Naseri A, Sirker J, Chakraborty T. Unique Spin Vortices and Topological Charges in Quantum Dots with Spin-orbit Couplings. Sci Rep 2019; 9:672. [PMID: 30679442 PMCID: PMC6345826 DOI: 10.1038/s41598-018-35837-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 11/06/2018] [Indexed: 11/11/2022] Open
Abstract
Spin textures of one or two electrons in a quantum dot with Rashba or Dresselhaus spin-orbit couplings reveal several intriguing properties. We show here that even at the single-electron level stable spin vortices with tunable topological charges exist. These topological textures appear in the ground state of the dots. The textures are stabilized by time-reversal symmetry breaking and are robust against the eccentricity of the dot. The topological charge is directly related to the sign of the z component of the spin in a large dot, allowing a direct probe of its topological properties. This would clearly pave the way to possible future topological spintronics. The phenomenon of spin vortices persists for the interacting two-electron dot in the presence of a magnetic field.
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Affiliation(s)
- Wenchen Luo
- Department of Physics, School of Physics and Electronics, Central South University, Changsha, Hunan, 410083, P. R. China
- Department of Physics and Astronomy, University of Manitoba, Winnipeg, R3T 2N2, Canada
| | - Amin Naseri
- Department of Physics and Astronomy, University of Manitoba, Winnipeg, R3T 2N2, Canada
| | - Jesko Sirker
- Department of Physics and Astronomy, University of Manitoba, Winnipeg, R3T 2N2, Canada.
| | - Tapash Chakraborty
- Department of Physics and Astronomy, University of Manitoba, Winnipeg, R3T 2N2, Canada
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18
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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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19
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Ravets S, Knüppel P, Faelt S, Cotlet O, Kroner M, Wegscheider W, Imamoglu A. Polaron Polaritons in the Integer and Fractional Quantum Hall Regimes. PHYSICAL REVIEW LETTERS 2018; 120:057401. [PMID: 29481149 DOI: 10.1103/physrevlett.120.057401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Revised: 11/26/2017] [Indexed: 06/08/2023]
Abstract
Elementary quasiparticles in a two-dimensional electron system can be described as exciton polarons since electron-exciton interactions ensures dressing of excitons by Fermi-sea electron-hole pair excitations. A relevant open question is the modification of this description when the electrons occupy flat bands and electron-electron interactions become prominent. Here, we perform cavity spectroscopy of a two-dimensional electron system in the strong coupling regime, where polariton resonances carry signatures of strongly correlated quantum Hall phases. By measuring the evolution of the polariton splitting under an external magnetic field, we demonstrate the modification of polaron dressing that we associate with filling factor dependent electron-exciton interactions.
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Affiliation(s)
- Sylvain Ravets
- Institute of Quantum Electroncis, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Patrick Knüppel
- Institute of Quantum Electroncis, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Stefan Faelt
- Institute of Quantum Electroncis, ETH Zürich, CH-8093 Zürich, Switzerland
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Ovidiu Cotlet
- Institute of Quantum Electroncis, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Martin Kroner
- Institute of Quantum Electroncis, ETH Zürich, CH-8093 Zürich, Switzerland
| | | | - Atac Imamoglu
- Institute of Quantum Electroncis, ETH Zürich, CH-8093 Zürich, Switzerland
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20
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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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21
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Kharkov YA, Sushkov OP, Mostovoy M. Bound States of Skyrmions and Merons near the Lifshitz Point. PHYSICAL REVIEW LETTERS 2017; 119:207201. [PMID: 29219354 DOI: 10.1103/physrevlett.119.207201] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Indexed: 06/07/2023]
Abstract
We study topological defects in anisotropic ferromagnets with competing interactions near the Lifshitz point. We show that Skyrmions and bimerons are stable in a large part of the phase diagram. We calculate Skyrmion-Skyrmion and meron-meron interactions and show that Skyrmions attract each other and form ring-shaped bound states in a zero magnetic field. At the Lifshitz point merons carrying a fractional topological charge become deconfined. These results imply that unusual topological excitations may exist in weakly frustrated magnets with conventional crystal lattices.
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Affiliation(s)
- Y A Kharkov
- School of Physics, University of New South Wales, Sydney 2052, Australia
| | - O P Sushkov
- School of Physics, University of New South Wales, Sydney 2052, Australia
| | - M Mostovoy
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, Netherlands
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22
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Hunt BM, Li JIA, Zibrov AA, Wang L, Taniguchi T, Watanabe K, Hone J, Dean CR, Zaletel M, Ashoori RC, Young AF. Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene. Nat Commun 2017; 8:948. [PMID: 29038518 PMCID: PMC5715057 DOI: 10.1038/s41467-017-00824-w] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 07/28/2017] [Indexed: 11/16/2022] Open
Abstract
The high magnetic field electronic structure of bilayer graphene is enhanced by the spin, valley isospin, and an accidental orbital degeneracy, leading to a complex phase diagram of broken symmetry states. Here, we present a technique for measuring the layer-resolved charge density, from which we directly determine the valley and orbital polarization within the zero energy Landau level. Layer polarization evolves in discrete steps across 32 electric field-tuned phase transitions between states of different valley, spin, and orbital order, including previously unobserved orbitally polarized states stabilized by skew interlayer hopping. We fit our data to a model that captures both single-particle and interaction-induced anisotropies, providing a complete picture of this correlated electron system. The resulting roadmap to symmetry breaking paves the way for deterministic engineering of fractional quantum Hall states, while our layer-resolved technique is readily extendable to other two-dimensional materials where layer polarization maps to the valley or spin quantum numbers. The phase diagram of bilayer graphene at high magnetic fields has been an outstanding question, with orders possibly between multiple internal quantum degrees of freedom. Here, Hunt et al. report the measurement of the valley and orbital order, allowing them to directly reconstruct the phase diagram.
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Affiliation(s)
- B M Hunt
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.,Department of Physics, Columbia University, New York, NY, 10027, USA.,Department of Physics, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
| | - J I A Li
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - A A Zibrov
- Department of Physics, University of California, Santa Barbara, CA, 93106, USA
| | - L Wang
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, 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
| | - J Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - C R Dean
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - M Zaletel
- Station Q, Microsoft Research, Santa Barbara, CA, 93106-6105, USA
| | - R C Ashoori
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - A F Young
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA. .,Department of Physics, University of California, Santa Barbara, CA, 93106, USA.
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23
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Li M, Wang J, Lu J. General planar transverse domain walls realized by optimized transverse magnetic field pulses in magnetic biaxial nanowires. Sci Rep 2017; 7:43065. [PMID: 28220893 PMCID: PMC5318861 DOI: 10.1038/srep43065] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/18/2017] [Indexed: 11/25/2022] Open
Abstract
The statics and field-driven dynamics of transverse domain walls (TDWs) in magnetic nanowires (NWs) have attracted continuous interests because of their theoretical significance and application potential in future magnetic logic and memory devices. Recent results demonstrate that uniform transverse magnetic fields (TMFs) can greatly enhance the wall velocity, meantime leave a twisting in the TDW azimuthal distribution. For application in high-density NW devices, it is preferable to erase the twisting so as to minimize magnetization frustrations. Here we report the realization of a completely planar TDW with arbitrary tilting attitude in a magnetic biaxial NW under a TMF pulse with fixed strength and well-designed orientation profile. We smooth any twisting in the TDW azimuthal plane thus completely decouple the polar and azimuthal degrees of freedom. The analytical differential equation describing the polar angle distribution is derived and the resulting solution is not the Walker-ansatz form. With this TMF pulse comoving, the field-driven dynamics of the planar TDW is investigated with the help of the asymptotic expansion method. It turns out the comoving TMF pulse increases the wall velocity under the same axial driving field. These results will help to design a series of modern magnetic devices based on planar TDWs.
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Affiliation(s)
- Mei Li
- School of Physics and Technology, Center for Electron Microscopy and MOE Key Laboratory of Artificial Micro- and Nano-structures, Wuhan University, Wuhan 430072, China
| | - Jianbo Wang
- School of Physics and Technology, Center for Electron Microscopy and MOE Key Laboratory of Artificial Micro- and Nano-structures, Wuhan University, Wuhan 430072, China
| | - Jie Lu
- College of Physics and Information Engineering, Hebei Advanced Thin Films Laboratory, Hebei Normal University, Shijiazhuang 050024, China
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24
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Moore JN, Hayakawa J, Mano T, Noda T, Yusa G. Optically Imaged Striped Domains of Nonequilibrium Electronic and Nuclear Spins in a Fractional Quantum Hall Liquid. PHYSICAL REVIEW LETTERS 2017; 118:076802. [PMID: 28256890 DOI: 10.1103/physrevlett.118.076802] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Indexed: 06/06/2023]
Abstract
Using photoluminescence microscopy enhanced by magnetic resonance, we visualize in real space both electron and nuclear polarization occurring in nonequilibrium fraction quantum Hall (FQH) liquids. We observe stripelike domain regions comprising FQH excited states which discretely form when the FQH liquid is excited by a source-drain current. These regions are deformable and give rise to bidirectionally polarized nuclear spins as spin-resolved electrons flow across their boundaries.
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Affiliation(s)
- John N Moore
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
| | | | - Takaaki Mano
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Takeshi Noda
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
| | - Go Yusa
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
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25
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Lian Y, Rosch A, Goerbig MO. SU(4) Skyrmions in the ν=±1 Quantum Hall State of Graphene. PHYSICAL REVIEW LETTERS 2016; 117:056806. [PMID: 27517789 DOI: 10.1103/physrevlett.117.056806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Indexed: 06/06/2023]
Abstract
We explore different Skyrmion types in the lowest Landau level of graphene at a filling factor ν=±1. In addition to the formation of spin and valley pseudospin Skyrmions, we show that another type of spin-valley entangled Skyrmions can be stabilized in graphene due to an approximate SU(4) spin-valley symmetry that is affected by sublattice symmetry-breaking terms. These Skyrmions have a clear signature in spin-resolved density measurements on the lattice scale, and we discuss the expected patterns for the different Skyrmion types.
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Affiliation(s)
- Y Lian
- Laboratoire de Physique des Solides, Univ. Paris-Sud, Université Paris-Saclay, CNRS, UMR 8502, F-91405 Orsay Cedex, France
| | - A Rosch
- Institut für Theoretische Physik, Universität zu Köln, D-50937 Cologne, Germany
| | - M O Goerbig
- Laboratoire de Physique des Solides, Univ. Paris-Sud, Université Paris-Saclay, CNRS, UMR 8502, F-91405 Orsay Cedex, France
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26
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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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27
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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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28
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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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29
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Moore E, Tycko R. Micron-scale magnetic resonance imaging of both liquids and solids. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 260:1-9. [PMID: 26397215 PMCID: PMC4628880 DOI: 10.1016/j.jmr.2015.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 08/31/2015] [Accepted: 09/02/2015] [Indexed: 05/16/2023]
Abstract
We describe and demonstrate a novel apparatus for magnetic resonance imaging (MRI), suitable for imaging of both liquid and solid samples with micron-scale isotropic resolution. The apparatus includes a solenoidal radio-frequency microcoil with 170 μm inner diameter and a set of planar gradient coils, all wound by hand and supported on a series of stacked sapphire plates. The design ensures efficient heat dissipation during gradient pulses and also facilitates disassembly, sample changes, and reassembly. To demonstrate liquid state (1)H MRI, we present an image of polystyrene beads within CuSO4-doped water, contained within a capillary tube with 100 μm inner diameter, with 5.0 μm isotropic resolution. To demonstrate solid state (1)H MRI, we present an image of NH4Cl particles within the capillary tube, with 8.0 μm isotropic resolution. High-resolution solid state MRI is enabled by frequency-switched Lee-Goldburg decoupling, with an effective rotating frame field amplitude of 289 kHz. At room temperature, pulsed gradients of 4 T/m (i.e., 170 Hz/μm for (1)H MRI) are achievable in all three directions with currents of 10 A or less. The apparatus is contained within a variable-temperature liquid helium cryostat, which will allow future efforts to obtain MRI images at low temperatures with signal enhancement by dynamic nuclear polarization.
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Affiliation(s)
- Eric Moore
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA
| | - Robert Tycko
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
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30
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Desrat W, Piot BA, Maude DK, Wasilewski ZR, Henini M, Airey R. W line shape in the resistively detected nuclear magnetic resonance. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:275801. [PMID: 26086605 DOI: 10.1088/0953-8984/27/27/275801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The resistively detected nuclear magnetic resonance (RDNMR) performed on a two-dimensional electron gas is known to exhibit a peculiar 'dispersive' line shape at some filling factors, especially around ν = 1. Here, we study in detail the inversion of the dispersive line shape as a function of the filling factor from ν = 1 to 2/3. The RDNMR spectra show a new characteristic W line shape in the longitudinal resistance, whereas dispersive lines detected in the Hall resistance remain unchanged. This W resonance, like the dispersive line, can be fitted correctly by a model of two independent response functions, which are the signatures of polarized and unpolarized electronic sub-systems.
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Affiliation(s)
- W Desrat
- Laboratoire Charles Coulomb, UMR 5221 CNRS-Université de Montpellier, Montpellier, France. Laboratoire National des Champs Magnétiques Intenses, CNRS-UJF-UPS-INSA, 38042 Grenoble, France
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31
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Tycko R. Remote sensing of sample temperatures in nuclear magnetic resonance using photoluminescence of semiconductor quantum dots. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 244:64-7. [PMID: 24859817 PMCID: PMC4090140 DOI: 10.1016/j.jmr.2014.04.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 04/30/2014] [Indexed: 05/22/2023]
Abstract
Knowledge of sample temperatures during nuclear magnetic resonance (NMR) measurements is important for acquisition of optimal NMR data and proper interpretation of the data. Sample temperatures can be difficult to measure accurately for a variety of reasons, especially because it is generally not possible to make direct contact to the NMR sample during the measurements. Here I show that sample temperatures during magic-angle spinning (MAS) NMR measurements can be determined from temperature-dependent photoluminescence signals of semiconductor quantum dots that are deposited in a thin film on the outer surface of the MAS rotor, using a simple optical fiber-based setup to excite and collect photoluminescence. The accuracy and precision of such temperature measurements can be better than ±5K over a temperature range that extends from approximately 50K (-223°C) to well above 310K (37°C). Importantly, quantum dot photoluminescence can be monitored continuously while NMR measurements are in progress. While this technique is likely to be particularly valuable in low-temperature MAS NMR experiments, including experiments involving dynamic nuclear polarization, it may also be useful in high-temperature MAS NMR and other forms of magnetic resonance.
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Affiliation(s)
- Robert Tycko
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States.
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32
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Abstract
Solid state nuclear magnetic resonance (NMR) measurements at low temperatures have been common in physical sciences for many years and are becoming increasingly important in studies of biomolecular systems. This Account reviews a diverse set of projects from my laboratory, dating back to the early 1990s, that illustrate the motivations for low-temperature solid state NMR, the types of information that are available from the measurements, and likely directions for future research. These projects include NMR studies of both physical and biological systems, performed at low (cooled with nitrogen, down to 77 K) and ultralow (cooled with helium, below 77 K) temperatures, and performed with and without magic-angle spinning (MAS). NMR studies of physical systems often focus on phenomena that occur only at low temperatures. Two examples from my laboratory are studies of molecular rotation and orientational ordering in solid C60 at low temperatures and studies of unusual electronic states, called skyrmions, in two-dimensionally confined electron systems within semiconductor quantum wells. To study quantum wells, we used optical pumping of nuclear spin polarizations to enhance their NMR signals. The optical pumping phenomenon exists only at ultralow temperatures. In studies of biomolecular systems, low-temperature NMR has several motivations. In some cases, low temperatures suppress molecular tumbling, thereby permitting solid state NMR measurements on soluble proteins. Studies of AIDS-related peptide/antibody complexes illustrate this effect. In other cases, low temperatures suppress conformational exchange, thereby permitting quantitation of conformational distributions. Studies of chemically denatured states of the model protein HP35 illustrate this effect. Low temperatures and rapid freeze-quenching can also be used to trap transient intermediate states in a non-equilibrium kinetic process, as shown in studies of a transient intermediate in the rapid folding pathway of HP35. NMR sensitivity generally increases with decreasing sample temperature. Therefore, it can be useful to carry out experiments at the lowest possible temperatures, particularly in studies of biomolecular systems in frozen solutions. However, solid state NMR studies of biomolecular systems generally require rapid MAS. A novel MAS NMR probe design that uses nitrogen gas for sample spinning and cold helium only for sample cooling allows a wide variety of solid state NMR measurements to be performed on biomolecular systems at 20-25 K, where signals are enhanced by factors of 12-15 relative to measurements at room temperature. MAS NMR at ultralow temperatures also facilitates dynamic nuclear polarization (DNP), allowing sizeable additional signal enhancements and large absolute NMR signal amplitudes with relatively low microwave powers. Current research in my laboratory seeks to develop and exploit DNP-enhanced MAS NMR at ultralow temperatures, for example, in studies of transient intermediates in protein folding and aggregation processes and studies of peptide/protein complexes that can be prepared only at low concentrations.
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Affiliation(s)
- Robert Tycko
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520
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Lin SZ, Reichhardt C, Batista CD, Saxena A. Driven Skyrmions and dynamical transitions in chiral magnets. PHYSICAL REVIEW LETTERS 2013; 110:207202. [PMID: 25167443 DOI: 10.1103/physrevlett.110.207202] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Revised: 03/21/2013] [Indexed: 06/03/2023]
Abstract
We study the dynamics of Skyrmions in chiral magnets in the presence of a spin polarized current. The motion of Skyrmions in the ferromagnetic background excites spin waves and contributes to additional damping. At a large current, the spin wave spectrum becomes gapless and Skyrmions are created dynamically from the ferromagnetic state. At an even higher current, these Skyrmions are strongly deformed due to the damping and become unstable at a threshold current, leading to a chiral liquid. We show how Skyrmions can be created by increasing the current in the magnetic spiral state. We then construct a dynamic phase diagram for a chiral magnet with a current. The instability transitions between different states can be observed as experimentally clear signatures in the transport measurements, such as jumps and hysteresis.
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Affiliation(s)
- Shi-Zeng Lin
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Charles Reichhardt
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Cristian D Batista
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Avadh Saxena
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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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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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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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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Karadimitriou ME, Kavousanaki EG, Dani KM, Fromer NA, Perakis IE. Strong electronic correlation effects in coherent multidimensional nonlinear optical spectroscopy. J Phys Chem B 2011; 115:5634-47. [PMID: 21395320 DOI: 10.1021/jp1118794] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We discuss a many-body theory of the coherent ultrafast nonlinear optical response of systems with a strongly correlated electronic ground state that responds unadiabatically to photoexcitation. We introduce a truncation of quantum kinetic density matrix equations of motion that does not rely on an expansion in terms of the interactions and thus applies to strongly correlated systems. For this we expand in terms of the optical field, separate out contributions to the time-evolved many-body state due to correlated and uncorrelated multiple optical transitions, and use "Hubbard operator" density matrices to describe the exact dynamics of the individual contributions within a subspace of strongly coupled states, including "pure dephasing". Our purpose is to develop a quantum mechanical tool capable of exploring how, by coherently photoexciting selected modes, one can trigger nonlinear dynamics of strongly coupled degrees of freedom. Such dynamics could lead to photoinduced phase transitions. We apply our theory to the nonlinear response of a two-dimensional electron gas (2DEG) in a magnetic field. We coherently photoexcite the two lowest Landau level (LL) excitations using three time-delayed optical pulses. We identify some striking temporal and spectral features due to dynamical coupling of the two LLs facilitated by inter-Landau-level magnetoplasmon and magnetoroton excitations and compare to three-pulse four-wave-mixing (FWM) experiments. We show that these features depend sensitively on the dynamics of four-particle correlations between an electron-hole pair and a magnetoplasmon/magnetoroton, reminiscent of exciton-exciton correlations in undoped semiconductors. Our results shed light into unexplored coherent dynamics and relaxation of the quantum Hall system (QHS) and can provide new insight into non-equilibrium co-operative phenomena in strongly correlated systems.
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Affiliation(s)
- M E Karadimitriou
- Department of Physics, University of Crete, Heraklion, Crete, 71003, Greece
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Becker S, Karrasch C, Mashoff T, Pratzer M, Liebmann M, Meden V, Morgenstern M. Probing electron-electron interaction in quantum Hall systems with scanning tunneling spectroscopy. PHYSICAL REVIEW LETTERS 2011; 106:156805. [PMID: 21568596 DOI: 10.1103/physrevlett.106.156805] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Indexed: 05/30/2023]
Abstract
Using low-temperature scanning tunneling spectroscopy applied to the Cs-induced two-dimensional electron system (2DES) on p-type InSb(110), we probe electron-electron interaction effects in the quantum Hall regime. The 2DES is decoupled from bulk states and exhibits spreading resistance within the insulating quantum Hall phases. In quantitative agreement with calculations we find an exchange enhancement of the spin splitting. Moreover, we observe that both the spatially averaged as well as the local density of states feature a characteristic Coulomb gap at the Fermi level. These results show that electron-electron interaction can be probed down to a resolution below all relevant length scales.
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Affiliation(s)
- S Becker
- II. Physikalisches Institut B and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany
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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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Fukuda JI. Stabilization of a blue phase by a guest component: an approach based on a Landau-de Gennes theory. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:061702. [PMID: 21230679 DOI: 10.1103/physreve.82.061702] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Revised: 10/24/2010] [Indexed: 05/30/2023]
Abstract
We discuss, with the aid of numerical calculations based on a Landau-de Gennes theory, the stabilization of a blue phase in chiral liquid crystals by introducing a guest component. Our argument is based on a common speculation that cores of disclination lines with higher free-energy density are replaced by the guest component. We assume that the guest component forms sharp interfaces with the liquid crystal (strong segregation). We show that, by a suitable choice of materials with small interfacial tension, a guest component of volume fraction less than 10% drastically increases the temperature range of thermodynamic stability of a blue phase, in agreement with experiments [Kikuchi, Nature Mater. 1, 64 (2002)].
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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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Fukuoka D, Oto K, Muro K, Hirayama Y, Kumada N. Skyrmion effect on the relaxation of spin waves in a quantum Hall ferromagnet. PHYSICAL REVIEW LETTERS 2010; 105:126802. [PMID: 20867665 DOI: 10.1103/physrevlett.105.126802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2009] [Indexed: 05/29/2023]
Abstract
Spin relaxation of two-dimensional electrons in a GaAs/AlGaAs quantum well was studied by time-resolved Kerr rotation measurements using a two-color pump and probe technique. In quantum Hall ferromagnets, the spin-wave relaxation is strongly influenced by the photogenerated Skyrmion and anti-Skyrmion pairs. By tuning the pump and probe lights to the lowest optical transition, an intrinsic filling factor dependence of spin relaxation is obtained without photogeneration of Skyrmions. The relaxation time of the spin wave presents a sharp peak at odd filling factors, accompanied by dips on both sides of it. The peculiar filling factor dependence of the spin-wave relaxation around quantum Hall ferromagnets can be explained by the interaction between the spin wave and Skyrmion. Observation of a similar feature around ν=1, 3, and 5 may suggest the existence of Skyrmions around higher odd filling factors.
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Affiliation(s)
- D Fukuoka
- Graduate School of Science, Chiba University, Chiba-shi, Chiba 263-8522, Japan
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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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Drozdov IK, Kulik LV, Zhuravlev AS, Kirpichev VE, Kukushkin IV, Schmult S, Dietsche W. Extra spin-wave mode in quantum Hall systems: beyond the Skyrmion limit. PHYSICAL REVIEW LETTERS 2010; 104:136804. [PMID: 20481903 DOI: 10.1103/physrevlett.104.136804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Indexed: 05/29/2023]
Abstract
We report on the observation of a new spin mode in a quantum Hall system in the vicinity of odd electron filling factors under experimental conditions excluding the possibility of Skyrmion excitations. The new mode having presumably zero energy at odd filling factors emerges at small deviations from odd filling factors and couples to the spin exciton. The existence of an extra spin mode assumes a nontrivial magnetic order at partial fillings of Landau levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.
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Affiliation(s)
- I K Drozdov
- Institute of Solid State Physics, RAS, Chernogolovka, 142432 Russia
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44
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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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45
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Reimer JA. Nuclear hyperpolarization in solids and the prospects for nuclear spintronics. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2010; 37:3-12. [PMID: 20413281 DOI: 10.1016/j.ssnmr.2010.04.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2010] [Accepted: 04/02/2010] [Indexed: 05/29/2023]
Abstract
Nuclear hyperpolarization can be achieved in a number of ways. This article focuses on the use of coupling of nuclei to (nearly) pure quantum states, with particular emphasis on those states obtained by optical excitation in bulk semiconductors. I seek an answer to this question: "What is to prevent the design and analysis of nuclear spintronics devices that use the extremely long-lived hyperpolarized nuclear spin states, and their weak couplings to each other, to affect computation, memory, or informational technology schemes?" The answer, I argue, is in part because there remains a lack of fundamental understanding of how to generate and control nuclear polarization with schemes other than with rf coils.
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Affiliation(s)
- Jeffrey A Reimer
- Department of Chemical Engineering, University of California Berkeley, Berkeley, CA 94720-1642, USA.
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46
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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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47
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Fukuda JI, Zumer S. Novel defect structures in a strongly confined liquid-crystalline blue phase. PHYSICAL REVIEW LETTERS 2010; 104:017801. [PMID: 20366394 DOI: 10.1103/physrevlett.104.017801] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Revised: 10/23/2009] [Indexed: 05/29/2023]
Abstract
In our numerical study based on a phenomenological description of strongly confined liquid crystalline blue phase I (BP I), we find several novel structures characterized by specific configurations of topological disclination lines. The thickness of the system is of the order of the dimension of the unit cell of the bulk BP I, and the confining surfaces adopts homeotropic anchoring. The structures include an array of double-helix disclination lines accompanied by an orthorhombic lattice of double-twist cylinders, and two parallel arrays of winding disclination lines almost perpendicular to each other.
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Affiliation(s)
- Jun-ichi Fukuda
- National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba 305-8568, Japan.
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48
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Van'kov AB, Kulik LV, Dickmann S, Kukushkin IV, Kirpichev VE, Dietsche W, Schmult S. Cyclotron spin-flip excitations in a nu = 1/3 quantum Hall ferromagnet. PHYSICAL REVIEW LETTERS 2009; 102:206802. [PMID: 19519061 DOI: 10.1103/physrevlett.102.206802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2009] [Indexed: 05/27/2023]
Abstract
Inelastic light scattering spectroscopy discloses a novel type of cyclotron spin-flip excitation in a quantum Hall system around the nu = 1/3 filling. The excitation energy follows qualitatively the degree of electron spin polarization, reaching a maximum value at nu = 1/3. This characterizes the new excitation as a nu = 1/3 ferromagnet eigenmode. The mode energy exceeds drastically the theoretical prediction obtained within the renowned single-mode approximation. We develop a new theoretical approach where the basis set is extended by adding a double-exciton component representing the cyclotron magnetoplasmon and spin wave coupled together. This double-mode approximation, inferred to be responsible for substantially reducing the gap between theoretical and experimental results, shows that the cyclotron spin-flip excitation is effectively a four-particle state.
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Affiliation(s)
- A B Van'kov
- Institute of Solid State Physics, RAS, Chernogolovka, 142432 Russia
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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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50
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Mui S, Ramaswamy K, Stanton CJ, Crooker SA, Hayes SE. Manifestation of Landau level effects in optically-pumped NMR of semi-insulating GaAs. Phys Chem Chem Phys 2009; 11:7031-5. [DOI: 10.1039/b907588g] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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