1
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Li Q, Chen Y, Wei L, Chen H, Huang Y, Zhu Y, Zhu W, An D, Song J, Gan Q, Zhang Q, Watanabe K, Taniguchi T, Shi X, Novoselov KS, Wang R, Yu G, Wang L. Strongly coupled magneto-exciton condensates in large-angle twisted double bilayer graphene. Nat Commun 2024; 15:5065. [PMID: 38871728 DOI: 10.1038/s41467-024-49406-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Accepted: 05/31/2024] [Indexed: 06/15/2024] Open
Abstract
Excitons, pairs of electrons and holes, undergo a Bose-Einstein condensation at low temperatures. An important platform to study excitons is double-layer two-dimensional electron gases, with two parallel planes of electrons and holes separated by a thin insulating layer. Lowering this separation (d) strengthens the exciton binding energy, however, leads to the undesired interlayer tunneling, resulting in annihilation of excitons. Here, we report the observation of a sequences of robust exciton condensates (ECs) in double bilayer graphene twisted to ~ 10° with no insulating mid-layer. The large momentum mismatch between two graphene layers suppresses interlayer tunneling, reaching a d ~ 0.334 nm. Measuring the bulk and edge transport, we find incompressible states corresponding to ECs when both layers are in half-filled N = 0, 1 Landau levels (LLs). Theoretical calculations suggest that the low-energy charged excitation of ECs can be meron-antimeron or particle-hole pair, which relies on both LL index and carrier type. Our results establish a novel platform with extreme coupling strength for studying quantum bosonic phase.
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Affiliation(s)
- Qingxin Li
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Yiwei Chen
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - LingNan Wei
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Hong Chen
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Yan Huang
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Yujian Zhu
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Wang Zhu
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Dongdong An
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Junwei Song
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Qikang Gan
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Qi Zhang
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Xiaoyang Shi
- Environmental and Sustainable Engineering, College of Engineering and Applied Science, University at Albany, Albany, NY, 12222, USA.
| | - Kostya S Novoselov
- Institute for Functional Intelligent Materials, National University of Singapore, Building S9, 4 Science Drive 2, Singapore, 117544, Singapore
| | - Rui Wang
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China.
| | - Geliang Yu
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China.
| | - Lei Wang
- National Laboratory of Solid-State Microstructures, School of Physics, Nanjing University, Nanjing, 210093, China.
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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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Nagase T, So YG, Yasui H, Ishida T, Yoshida HK, Tanaka Y, Saitoh K, Ikarashi N, Kawaguchi Y, Kuwahara M, Nagao M. Observation of domain wall bimerons in chiral magnets. Nat Commun 2021; 12:3490. [PMID: 34108478 PMCID: PMC8190141 DOI: 10.1038/s41467-021-23845-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 05/19/2021] [Indexed: 12/03/2022] Open
Abstract
Topological defects embedded in or combined with domain walls have been proposed in various systems, some of which are referred to as domain wall skyrmions or domain wall bimerons. However, the experimental observation of such topological defects remains an ongoing challenge. Here, using Lorentz transmission electron microscopy, we report the experimental discovery of domain wall bimerons in chiral magnet Co-Zn-Mn(110) thin films. By applying a magnetic field, multidomain structures develop, and simultaneously, chained or isolated bimerons arise as the localized state between the domains with the opposite in-plane components of net magnetization. The multidomain formation is attributed to magnetic anisotropy and dipolar interaction, and domain wall bimerons are stabilized by the Dzyaloshinskii-Moriya interaction. In addition, micromagnetic simulations show that domain wall bimerons appear for a wide range of conditions in chiral magnets with cubic magnetic anisotropy. Our results promote further study in various fields of physics.
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Affiliation(s)
- Tomoki Nagase
- Department of Electronics, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
| | - Yeong-Gi So
- Department of Materials Science, Graduate School of Engineering Science, Akita University, Akita, Japan
| | - Hayata Yasui
- Department of Materials Science, Graduate School of Engineering Science, Akita University, Akita, Japan
| | - Takafumi Ishida
- Advanced Measurement Technology Center, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Hiroyuki K Yoshida
- Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Japan
| | - Yukio Tanaka
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Koh Saitoh
- Advanced Measurement Technology Center, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Nobuyuki Ikarashi
- Department of Electronics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
- Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan
| | - Yuki Kawaguchi
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan
| | - Makoto Kuwahara
- Advanced Measurement Technology Center, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan.
- Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
| | - Masahiro Nagao
- Department of Electronics, Graduate School of Engineering, Nagoya University, Nagoya, Japan.
- Center for Integrated Research of Future Electronics, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan.
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4
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Lu TM, Tracy LA, Laroche D, Huang SH, Chuang Y, Su YH, Li JY, Liu CW. Density-controlled quantum Hall ferromagnetic transition in a two-dimensional hole system. Sci Rep 2017; 7:2468. [PMID: 28572640 PMCID: PMC5453979 DOI: 10.1038/s41598-017-02757-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 04/18/2017] [Indexed: 11/10/2022] Open
Abstract
Quantum Hall ferromagnetic transitions are typically achieved by increasing the Zeeman energy through in-situ sample rotation, while transitions in systems with pseudo-spin indices can be induced by gate control. We report here a gate-controlled quantum Hall ferromagnetic transition between two real spin states in a conventional two-dimensional system without any in-plane magnetic field. We show that the ratio of the Zeeman splitting to the cyclotron gap in a Ge two-dimensional hole system increases with decreasing density owing to inter-carrier interactions. Below a critical density of ~2.4 × 1010 cm−2, this ratio grows greater than 1, resulting in a ferromagnetic ground state at filling factor ν = 2. At the critical density, a resistance peak due to the formation of microscopic domains of opposite spin orientations is observed. Such gate-controlled spin-polarizations in the quantum Hall regime opens the door to realizing Majorana modes using two-dimensional systems in conventional, low-spin-orbit-coupling semiconductors.
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Affiliation(s)
- T M Lu
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA.
| | - L A Tracy
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
| | - D Laroche
- Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
| | - S-H Huang
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - Y Chuang
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - Y-H Su
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - J-Y Li
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
| | - C W Liu
- Department of Electrical Engineering and Graduate Institute of Electronic Engineering, National Taiwan University, Taipei, 10617, Taiwan, ROC.,National Nano Device Laboratories, Hsinchu, 30077, Taiwan, ROC
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5
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Datta B, Dey S, Samanta A, Agarwal H, Borah A, Watanabe K, Taniguchi T, Sensarma R, Deshmukh MM. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene. Nat Commun 2017; 8:14518. [PMID: 28216666 PMCID: PMC5321728 DOI: 10.1038/ncomms14518] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 01/06/2017] [Indexed: 11/09/2022] Open
Abstract
Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm2 V−1 s−1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree–Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field. Few-layered graphene offers a powerful platform to investigate electronic interactions beyond the non-interacting electron picture approximation. Here, the authors report the signature of strong electronic interactions and quantum Hall ferromagnetism in trilayer graphene with ABA stacking.
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Affiliation(s)
- Biswajit Datta
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Santanu Dey
- Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Abhisek Samanta
- Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Hitesh Agarwal
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Abhinandan Borah
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Rajdeep Sensarma
- Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
| | - Mandar M Deshmukh
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India
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6
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Nuebler J, Friess B, Umansky V, Rosenow B, Heiblum M, von Klitzing K, Smet J. Quantized ν = 5/2 state in a two-subband quantum hall system. PHYSICAL REVIEW LETTERS 2012; 108:046804. [PMID: 22400875 DOI: 10.1103/physrevlett.108.046804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Indexed: 05/31/2023]
Abstract
The evolution of the fractional quantum Hall state at filling 5/2 is studied in density tunable two-dimensional electron systems formed in wide wells in which it is possible to induce a transition from single- to two-subband occupancy. In 80 and 60 nm wells, the quantum Hall state at 5/2 filling of the lowest subband is observed even when the second subband is occupied. In a 50 nm well, the 5/2 state vanishes upon second subband population. We attribute this distinct behavior to the width dependence of the capacitive energy for intersubband charge transfer and of the overlap of the subband probability densities.
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Affiliation(s)
- J Nuebler
- Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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7
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Liu Y, Shabani J, Kamburov D, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. Evolution of the 7/2 fractional quantum Hall state in two-subband systems. PHYSICAL REVIEW LETTERS 2011; 107:266802. [PMID: 22243175 DOI: 10.1103/physrevlett.107.266802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Indexed: 05/31/2023]
Abstract
We report the evolution of the fractional quantum Hall state (FQHS) at a total Landau level (LL) filling factor of ν=7/2 in wide GaAs quantum wells in which electrons occupy two electric subbands. The data reveal subtle and distinct evolutions as a function of density, magnetic field tilt angle, or symmetry of the charge distribution. At intermediate tilt angles, for example, we observe a strengthening of the ν=7/2 FQHS. Moreover, in a well with asymmetric change distribution, there is a developing FQHS when the LL filling factor of the symmetric subband ν(S) equals 5/2 while the antisymmetric subband has a filling factor of 1<ν(A)<2.
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Affiliation(s)
- Yang Liu
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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8
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Shabani J, Liu Y, Shayegan M. Fractional quantum Hall effect at high fillings in a two-subband electron system. PHYSICAL REVIEW LETTERS 2010; 105:246805. [PMID: 21231548 DOI: 10.1103/physrevlett.105.246805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Indexed: 05/30/2023]
Abstract
Magnetotransport measurements in a clean two-dimensional electron system confined to a wide GaAs quantum well reveal that, when the electrons occupy two electric subbands, the sequences of fractional quantum Hall states observed at high fillings (ν>2) are distinctly different from those of a single-subband system. Notably, when the Fermi energy lies in the ground state Landau level of either of the subbands, no quantum Hall states are seen at the even-denominator ν=5/2 and 7/2 fillings; instead, the observed states are at ν=[i+p/(2p±1)], where i=2, 3, 4 and p=1, 2, 3, and include several new states at ν=13/5, 17/5, 18/5, 25/7, and 14/3.
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Affiliation(s)
- J Shabani
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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9
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Ferreira GJ, Freire HJP, Egues JC. Many-body effects on the rho(xx) ringlike structures in two-subband wells. PHYSICAL REVIEW LETTERS 2010; 104:066803. [PMID: 20366846 DOI: 10.1103/physrevlett.104.066803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Indexed: 05/29/2023]
Abstract
The longitudinal resistivity rho(xx) of two-dimensional electron gases formed in wells with two subbands displays ringlike structures when plotted in a density-magnetic-field diagram, due to the crossings of spin-split Landau levels (LLs) from distinct subbands. Using spin density functional theory and linear response, we investigate the shape and spin polarization of these structures as a function of temperature and magnetic-field tilt angle. We find that (i) some of the rings "break" at sufficiently low temperatures due to a quantum Hall ferromagnetic phase transition, thus exhibiting a high degree of spin polarization (approximately 50%) within, consistent with the NMR data of Zhang et al. [Phys. Rev. Lett. 98, 246802 (2007)], and (ii) for increasing tilting angles the interplay between the anticrossings due to inter-LL couplings and the exchange-correlation effects leads to a collapse of the rings at some critical angle theta(c), in agreement with the data of Guo et al. [Phys. Rev. B 78, 233305 (2008)].
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Affiliation(s)
- Gerson J Ferreira
- Departamento de Física e Informática, Instituto de Física de São Carlos, Universidade de São Paulo, 13560-970 São Carlos, São Paulo, Brazil
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10
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Hao XJ, Tu T, Cao G, Guo GC, Jiang HW, Guo GP. Phase diagram of a quantum Hall pseudospin ferromagnet in a two-subband electron system. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:455802. [PMID: 21694020 DOI: 10.1088/0953-8984/21/45/455802] [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 employ the self-consistent local density approximation and the microscopic Hartree-Fock theory to investigate the quantum Hall pseudospin ferromagnets at the Landau levels degenerate regime of a single quantum well with two-subbands filled. We carry out a detailed calculation of the pseudospin anisotropy energy using real experimental parameters and obtain the phase diagrams that would be accessed experimentally by changing the electron density and the bias voltage. We find that an easy-plane and easy-axis quantum Hall pseudospin ferromagnet can form at total filling factors ν = 3 and ν = 4, respectively, which are consistent with experimental observation. Our study provides some insight into the symmetry of the ground state and may help in understanding the underlying mechanism.
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Affiliation(s)
- Xiao-Jie Hao
- Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026, People's Republic of China
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11
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Toyama K, Nishioka T, Sawano K, Shiraki Y, Okamoto T. Electronic transport properties of the Ising quantum Hall ferromagnet in a Si quantum well. PHYSICAL REVIEW LETTERS 2008; 101:016805. [PMID: 18764140 DOI: 10.1103/physrevlett.101.016805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Indexed: 05/26/2023]
Abstract
Magnetotransport properties are investigated for a high mobility Si two-dimensional electron system in the vicinity of a Landau level crossing point. At low temperatures, the resistance peak having a strong anisotropy shows large hysteresis which is attributed to Ising quantum Hall ferromagnetism. The peak is split into two peaks in the paramagnetic regime. A mean field calculation for the peak positions indicates that electron scattering is strong when the pseudospin is partially polarized. We also study the current-voltage characteristics which exhibit a wide voltage plateau.
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Affiliation(s)
- Kiyohiko Toyama
- Department of Physics, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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12
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Khrapai VS, Shashkin AA, Trokina MG, Dolgopolov VT, Pellegrini V, Beltram F, Biasiol G, Sorba L. Direct measurements of fractional quantum Hall effect gaps. PHYSICAL REVIEW LETTERS 2007; 99:086802. [PMID: 17930970 DOI: 10.1103/physrevlett.99.086802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Indexed: 05/25/2023]
Abstract
We measure the chemical potential jump across the fractional gap in the low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs single heterojunctions. In the fully spin-polarized regime, the gap for filling factor nu=1/3 increases linearly with the magnetic field and is coincident with that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau level. In low magnetic fields, at the ground-state spin transition for nu=2/3, a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed.
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Affiliation(s)
- V S Khrapai
- Institute of Solid State Physics, Chernogolovka, Moscow District, Russia
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13
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Takashina K, Brun M, Ota T, Maude DK, Fujiwara A, Ono Y, Takahashi Y, Hirayama Y. Anomalous resistance ridges along filling factor nu=4i. PHYSICAL REVIEW LETTERS 2007; 99:036803. [PMID: 17678309 DOI: 10.1103/physrevlett.99.036803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Indexed: 05/16/2023]
Abstract
We report anomalous structure in the magnetoresistance of SiO(2)/Si(100)/SiO(2) quantum wells. When Landau levels of opposite valleys are driven through coincidence at the Fermi level, the longitudinal resistance displays elevations at filling factors that are integer multiples of 4 (nu=4i) accompanied by suppression on either side of nu=4i. This persists when either the magnetic field or the valley splitting is swept, leading to resistance ridges running along nu=4i. The range of field over which they are observed points to the role of spin degeneracy, which is directly confirmed by their disappearance with the addition of an in-plane magnetic field. The data suggest a new type of many-body effect arising from the combined degeneracy due to the valley and the spin degrees of freedom.
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Affiliation(s)
- K Takashina
- NTT Basic Research Laboratories, NTT Corporation, Atsugi-shi, Kanagawa 243-0198, Japan
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14
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Zhang XC, Scott GD, Jiang HW. NMR probing of spin excitations in the ring structure of a two-subband system. PHYSICAL REVIEW LETTERS 2007; 98:246802. [PMID: 17677981 DOI: 10.1103/physrevlett.98.246802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Indexed: 05/16/2023]
Abstract
Resistively detected nuclear magnetic resonance (NMR) is observed inside the ringlike structure, with a quantized Hall conductance of 6e(2)/h, in the phase diagram of a two-subband electron system. The NMR signal persists up to 470 mK and is absent in other states with the same quantized Hall conductance. The nuclear spin-lattice relaxation time T1, is found to decrease rapidly towards the ring center. A strong dynamic nuclear polarization by the biasing current has also been observed only inside the ring. These observations are consistent with the assertion of the ringlike region being a ferromagnetic state that is accompanied by collective spin excitations.
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Affiliation(s)
- X C Zhang
- Department of Physics and Astronomy, University of California at Los Angeles, 405 Hilgard Avenue, Los Angeles, California 90095, USA
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15
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Vakili K, Gokmen T, Gunawan O, Shkolnikov YP, De Poortere EP, Shayegan M. Dependence of persistent gaps at landau level crossings on relative spin. PHYSICAL REVIEW LETTERS 2006; 97:116803. [PMID: 17025916 DOI: 10.1103/physrevlett.97.116803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Indexed: 05/12/2023]
Abstract
We report measurements of the quantum Hall state energy gap at avoided crossings between Landau levels originating from different conduction band valleys in AlAs quantum wells. These gaps exhibit an approximately linear dependence on the magnetic field over a wide range of fields and filling factors. More remarkably, we observe an unexpected dependence of the gap size on the relative spin orientation of the crossing levels, with parallel-spin crossings exhibiting larger gaps than antiparallel-spin crossings.
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Affiliation(s)
- K Vakili
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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16
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Abstract
Resistively detected nuclear spin relaxation measurements in closely separated two-dimensional electron systems reveal strong low-frequency electron-spin fluctuations in the quantum Hall regime. As the temperature is decreased, the spin fluctuations, manifested by a sharp enhancement of the nuclear spin-lattice relaxation rate 1/T1, continue to grow down to the lowest temperature of 66 millikelvin. The observed divergent behavior of 1/T1 signals a gapless spin excitation mode and is a hallmark of canted antiferromagnetic order. Our data demonstrate the realization of a two-dimensional system with planar broken symmetry, in which fluctuations do not freeze out when approaching the zero temperature limit.
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Affiliation(s)
- Norio Kumada
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
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17
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Lai K, Pan W, Tsui DC, Lyon S, Mühlberger M, Schäffler F. Intervalley gap anomaly of two-dimensional electrons in silicon. PHYSICAL REVIEW LETTERS 2006; 96:076805. [PMID: 16606125 DOI: 10.1103/physrevlett.96.076805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Indexed: 05/08/2023]
Abstract
We report here a systematic study of the energy gaps at the odd-integer quantum Hall states nu = 3 and 5 under tilted magnetic (B) fields in a high quality Si two-dimensional electron system. Out of the coincidence region, the valley splitting is independent of the in-plane fields. However, the nu = 3 valley gap differs by about a factor of 3 (Deltav approximately 0.4 vs 1.2 K) on different sides of the coincidence. More surprisingly, instead of reducing to zero, the energy gaps at nu = 3 and 5 rise rapidly when approaching the coincidence angles. We believe that such an anomaly is related to strong couplings of the nearly degenerate Landau levels.
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Affiliation(s)
- K Lai
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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18
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Rossi E, Núñez AS, MacDonald AH. Interlayer transport in bilayer quantum Hall systems. PHYSICAL REVIEW LETTERS 2005; 95:266804. [PMID: 16486385 DOI: 10.1103/physrevlett.95.266804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Indexed: 05/06/2023]
Abstract
Bilayer quantum Hall systems have a broken symmetry ground state at a filling factor which can be viewed either as an excitonic superfluid or as a pseudospin ferromagnet. We present a theory of interlayer transport in quantum Hall bilayers that highlights remarkable similarities and critical differences between transport in Josephson junction and ferromagnetic metal spin-transfer devices. Our theory is able to explain the size of the large but finite low-bias interlayer conductance and the voltage width of this collective transport anomaly.
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Affiliation(s)
- Enrico Rossi
- Department of Physics, University of Texas at Austin, 78712, USA
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19
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De Poortere EP, Tutuc E, Shayegan M. Critical resistance in the AlAs quantum Hall ferromagnet. PHYSICAL REVIEW LETTERS 2003; 91:216802. [PMID: 14683327 DOI: 10.1103/physrevlett.91.216802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2003] [Indexed: 05/24/2023]
Abstract
Magnetic transitions in AlAs two-dimensional electrons give rise to sharp resistance spikes within the quantum Hall effect. Such spikes are likely caused by carrier scattering at magnetic domain walls below the Curie temperature. We report a critical behavior in the temperature dependence of the spike width and amplitude, from which we deduce the Curie temperature of the quantum Hall ferromagnet. Our data also reveal that the Curie temperature increases monotonically with carrier density.
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Affiliation(s)
- E P De Poortere
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA
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20
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Jaroszyński J, Andrearczyk T, Karczewski G, Wróbel J, Wojtowicz T, Papis E, Kamińska E, Piotrowska A, Popović D, Dietl T. Ising quantum Hall ferromagnet in magnetically doped quantum wells. PHYSICAL REVIEW LETTERS 2002; 89:266802. [PMID: 12484847 DOI: 10.1103/physrevlett.89.266802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2002] [Indexed: 05/24/2023]
Abstract
We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T(C) as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance "spikes" at T-->T(C) corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.
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Affiliation(s)
- J Jaroszyński
- Institute of Physics, Polish Academy of Sciences, aleja Lotników 32/46, 02-668 Warszawa, Poland.
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