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Dorozhkin SI, Umansky V, Pfeiffer LN, West KW, Baldwin K, von Klitzing K, Smet JH. Random flips of electric field in microwave-induced states with spontaneously broken symmetry. PHYSICAL REVIEW LETTERS 2015; 114:176808. [PMID: 25978254 DOI: 10.1103/physrevlett.114.176808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Indexed: 06/04/2023]
Abstract
In a two-dimensional electron system subject to microwaves and a magnetic field, photovoltages emerge. They can be separated into two components originating from built-in electric fields and electric field domains arising from spontaneous symmetry breaking. The latter occurs in the zero resistance regime only and manifests itself in pulsed behavior, synchronous across the sample. The pulses show sign reversal. This implies a flip of the field in each domain, consistent with the existence of two equally probable electric field domain configurations due to the spontaneous symmetry breaking.
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Kleinbaum E, Kumar A, Pfeiffer LN, West KW, Csáthy GA. Gap reversal at filling factors 3+1/3 and 3+1/5: towards novel topological order in the fractional quantum Hall regime. PHYSICAL REVIEW LETTERS 2015; 114:076801. [PMID: 25763967 DOI: 10.1103/physrevlett.114.076801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Indexed: 06/04/2023]
Abstract
In the region of the second Landau level several theories predict fractional quantum Hall states with novel topological order. We report the opening of an energy gap at the filling factor ν=3+1/3, firmly establishing the ground state as a fractional quantum Hall state. This and other odd-denominator states unexpectedly break particle-hole symmetry. Specifically, we find that the relative magnitudes of the energy gaps of the ν=3+1/3 and 3+1/5 states from the upper spin branch are reversed when compared to the ν=2+1/3 and 2+1/5 counterpart states in the lower spin branch. Our findings raise the possibility that at least one of the former states is of an unusual topological order.
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Liu Y, Kamburov D, Hasdemir S, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. Fractional quantum Hall effect and Wigner crystal of interacting composite fermions. PHYSICAL REVIEW LETTERS 2014; 113:246803. [PMID: 25541794 DOI: 10.1103/physrevlett.113.246803] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Indexed: 06/04/2023]
Abstract
In two-dimensional electron systems confined to GaAs quantum wells, as a function of either tilting the sample in a magnetic field or increasing density, we observe multiple spin-polarization transitions of the fractional quantum Hall states at filling factors ν=4/5 and 5/7. The number of observed transitions provides evidence that these are fractional quantum Hall states of interacting two-flux composite fermions. Moreover, the fact that the reentrant integer quantum Hall effect near ν=4/5 always develops following the transition to full spin polarization of the ν=4/5 fractional quantum Hall state links the reentrant phase to a pinned ferromagnetic Wigner crystal of composite fermions.
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Kamburov D, Liu Y, Mueed MA, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. What determines the Fermi wave vector of composite fermions? PHYSICAL REVIEW LETTERS 2014; 113:196801. [PMID: 25415915 DOI: 10.1103/physrevlett.113.196801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Indexed: 06/04/2023]
Abstract
Composite fermions (CFs), exotic particles formed by pairing an even number of flux quanta to each electron, provide a fascinating description of phenomena exhibited by interacting two-dimensional electrons at high magnetic fields. At and near Landau level filling ν=1/2, CFs occupy a Fermi sea and exhibit commensurability effects when subjected to a periodic potential modulation. We observe a pronounced asymmetry in the magnetic field positions of the commensurability resistance minima of CFs with respect to the field at ν=1/2. This unexpected asymmetry is consistent with the CFs' Fermi wave vector being determined by the minority carriers in the lowest Landau level, and suggests a breaking of the particle-hole symmetry for CFs near ν=1/2.
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Scheller CP, Liu TM, Barak G, Yacoby A, Pfeiffer LN, West KW, Zumbühl DM. Possible evidence for helical nuclear spin order in GaAs quantum wires. PHYSICAL REVIEW LETTERS 2014; 112:066801. [PMID: 24580700 DOI: 10.1103/physrevlett.112.066801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2013] [Indexed: 06/03/2023]
Abstract
We present transport measurements of cleaved edge overgrowth GaAs quantum wires. The conductance of the first mode reaches 2e(2)/h at high temperatures T≳10 K, as expected. As T is lowered, the conductance is gradually reduced to 1e(2)/h, becoming T independent at T≲0.1 K, while the device cools far below 0.1 K. This behavior is seen in several wires, is independent of density, and not altered by moderate magnetic fields B. The conductance reduction by a factor of 2 suggests lifting of the electron spin degeneracy in the absence of B. Our results are consistent with theoretical predictions for helical nuclear magnetism in the Luttinger liquid regime.
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56
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Liu Y, Graninger AL, Hasdemir S, Shayegan M, Pfeiffer LN, West KW, Baldwin KW, Winkler R. Fractional quantum Hall effect at ν=1/2 in hole systems confined to GaAs quantum wells. PHYSICAL REVIEW LETTERS 2014; 112:046804. [PMID: 24580479 DOI: 10.1103/physrevlett.112.046804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Indexed: 06/03/2023]
Abstract
We observe the fractional quantum Hall effect (FQHE) at the even-denominator Landau level filling factor ν=1/2 in two-dimensional hole systems confined to GaAs quantum wells of width 30 to 50 nm and having bilayerlike charge distributions. The ν=1/2 FQHE is stable when the charge distribution is symmetric and only in a range of intermediate densities, qualitatively similar to what is seen in two-dimensional electron systems confined to approximately twice wider GaAs quantum wells. Despite the complexity of the hole Landau level structure, originating from the coexistence and mixing of the heavy- and light-hole states, we find the hole ν=1/2 FQHE to be consistent with a two-component, Halperin-Laughlin (Ψ331) state.
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57
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Huang J, Pfeiffer LN, West KW. Influence of Coulomb interaction of tunable shapes on the collective transport of ultradilute two-dimensional holes. PHYSICAL REVIEW LETTERS 2014; 112:036803. [PMID: 24484159 DOI: 10.1103/physrevlett.112.036803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Indexed: 06/03/2023]
Abstract
In high quality updoped GaAs field-effect transistors, the two-dimensional charge carrier concentrations can be tuned to very low values similar to the density of electrons on helium surfaces. An important interaction effect, screening of the Coulomb interaction by the gate, rises as a result of the large charge spacing comparable to the distance between the channel and the gate. Based on the results of the temperature (T) dependence of the resistivity from measuring four different samples, a power-law characteristic is found for charge densities ≤2×10(9) cm(-2). Moreover, the exponent exhibits a universal dependence on a single dimensionless parameter, the ratio between the mean carrier separation and the distance to the metallic gate that screens the Coulomb interaction. Thus, the electronic properties are tuned through varying the shape of the interaction potential.
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58
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Willett RL, Nayak C, Shtengel K, Pfeiffer LN, West KW. Magnetic-field-tuned Aharonov-Bohm oscillations and evidence for non-Abelian anyons at ν = 5/2. PHYSICAL REVIEW LETTERS 2013; 111:186401. [PMID: 24237543 DOI: 10.1103/physrevlett.111.186401] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Indexed: 06/02/2023]
Abstract
We show that the resistance of the ν = 5/2 quantum Hall state, confined to an interferometer, oscillates with the magnetic field consistent with an Ising-type non-Abelian state. In three quantum Hall interferometers of different sizes, resistance oscillations at ν = 7/3 and integer filling factors have the magnetic field period expected if the number of quasiparticles contained within the interferometer changes so as to keep the area and the total charge within the interferometer constant. Under these conditions, an Abelian state such as the (3, 3, 1) state would show oscillations with the same period as at an integer quantum Hall state. However, in an Ising-type non-Abelian state there would be a rapid oscillation associated with the "even-odd effect" and a slower one associated with the accumulated Abelian phase due to both the Aharonov-Bohm effect and the Abelian part of the quasiparticle braiding statistics. Our measurements at ν = 5/2 are consistent with the latter.
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59
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Shinokita K, Hirori H, Tanaka K, Mochizuki T, Kim C, Akiyama H, Pfeiffer LN, West KW. Terahertz-induced optical emission of photoexcited undoped GaAs quantum wells. PHYSICAL REVIEW LETTERS 2013; 111:067401. [PMID: 23971609 DOI: 10.1103/physrevlett.111.067401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2012] [Indexed: 06/02/2023]
Abstract
Intense terahertz (THz) pulse induces photoluminescence (PL) flash from undoped high-quality GaAs/AlGaAs quantum wells under continuous wave laser excitation. The number of excitons increases 10,000-fold from that of the steady state under only laser excitation. The THz electric field dependence and the relaxation dynamics of the PL flash intensity suggest that the strong electric field of the THz pulse ionizes impurity states during the 1 ps period of the THz pulse and release carriers from a giant reservoir containing impurity states in the AlGaAs layers.
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60
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Kamburov D, Liu Y, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. Composite fermions with tunable Fermi contour anisotropy. PHYSICAL REVIEW LETTERS 2013; 110:206801. [PMID: 25167436 DOI: 10.1103/physrevlett.110.206801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Indexed: 06/03/2023]
Abstract
The composite fermion formalism elegantly describes some of the most fascinating behaviors of interacting two-dimensional carriers at low temperatures and in strong perpendicular magnetic fields. In this framework, carriers minimize their energy by attaching two flux quanta and forming new quasiparticles, the so-called composite fermions. Thanks to the flux attachment, when a Landau level is half-filled, the composite fermions feel a vanishing effective magnetic field and possess a Fermi surface with a well-defined Fermi contour. Our measurements in a high-quality two-dimensional hole system confined to a GaAs quantum well demonstrate that a parallel magnetic field can significantly distort the hole-flux composite fermion Fermi contour.
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61
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Wurstbauer U, West KW, Pfeiffer LN, Pinczuk A. Resonant inelastic light scattering investigation of low-lying gapped excitations in the quantum fluid at ν=5/2. PHYSICAL REVIEW LETTERS 2013; 110:026801. [PMID: 23383929 DOI: 10.1103/physrevlett.110.026801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Indexed: 05/06/2023]
Abstract
The low-lying neutral excitation spectrum of the incompressible quantum Hall fluid at ν=5/2 is investigated by inelastic light scattering. Gapped modes are observable only in a very narrow filling factor range centered at 5/2 at energies that overlap estimates from transport activation gaps. The modes are interpreted as critical points in the wave-vector dispersion of excitations that preserve spin orientation. For very small changes |δν|≲0.01 the gapped modes disappear and a continuum of low-lying excitations takes over indicating the transition from an incompressible fluid at 5/2 to a compressible state. Observations of spin wave modes indicate spin polarization of the 5/2 and 2+1/3 quantum Hall fluids.
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62
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Kamburov D, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. Commensurability oscillations of hole-flux composite fermions. PHYSICAL REVIEW LETTERS 2012; 109:236401. [PMID: 23368228 DOI: 10.1103/physrevlett.109.236401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Indexed: 06/01/2023]
Abstract
We report the observation of commensurability oscillations of hole-flux composite fermions near a filling factor of ν=1/2 in a high-mobility two-dimensional hole system confined to a GaAs quantum well and subjected to a weak, strain-induced, unidirectional periodic potential modulation. The oscillations, which are consistent with ballistic transport of fully spin-polarized composite fermions in a weak periodic effective magnetic field, are surprisingly strong and exhibit up to third-order minima. We extract a ballistic mean-free path of about 0.1 μm for the hole-flux composite fermions.
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63
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Liu Y, Pappas CG, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. Observation of reentrant integer quantum Hall states in the lowest Landau level. PHYSICAL REVIEW LETTERS 2012; 109:036801. [PMID: 22861882 DOI: 10.1103/physrevlett.109.036801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 02/13/2012] [Indexed: 06/01/2023]
Abstract
Measurements on very low disorder two-dimensional electrons confined to relatively wide GaAs quantum well samples with tunable density reveal a close competition between the electron liquid and solid phases near the Landau level filling factor ν=1. As the density is raised, the fractional quantum Hall liquid at ν=4/5 suddenly disappears at a well-width dependent critical density, and then reappears at higher densities with insulating phases on its flanks. These insulating phases exhibit reentrant ν=1 integer quantum Hall effects and signal the formation of electron Wigner crystal states. Qualitatively similar phenomena are seen near ν=6/5.
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64
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Kou A, Marcus CM, Pfeiffer LN, West KW. Coulomb oscillations in antidots in the integer and fractional quantum Hall regimes. PHYSICAL REVIEW LETTERS 2012; 108:256803. [PMID: 23004632 DOI: 10.1103/physrevlett.108.256803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2012] [Indexed: 06/01/2023]
Abstract
We report measurements of resistance oscillations in micron-scale antidots in both the integer and fractional quantum Hall regimes. In the integer regime, we conclude that oscillations are of the Coulomb type from the scaling of magnetic field period with the number of edges bound to the antidot. Based on both gate-voltage and field periods, we find at filling factor ν = 2 a tunneling charge of e and two charged edges. Generalizing this picture to the fractional regime, we find (again, based on field and gate-voltage periods) at ν = 2/3 a tunneling charge of (2/3)e and a single charged edge.
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65
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McClure DT, Chang W, Marcus CM, Pfeiffer LN, West KW. Fabry-Perot interferometry with fractional charges. PHYSICAL REVIEW LETTERS 2012; 108:256804. [PMID: 23004633 DOI: 10.1103/physrevlett.108.256804] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Indexed: 06/01/2023]
Abstract
Resistance oscillations in electronic Fabry-Perot interferometers near fractional quantum Hall (FQH) filling factors 1/3, 2/3, 4/3, and 5/3 in the constrictions are compared to those near integer quantum Hall (IQH) filling factors in the same devices and at the same gate voltages. Two-dimensional plots of resistance versus gate voltage and magnetic field indicate that all oscillations are Coulomb dominated. A charging-model analysis of gate-voltage periods yields an effective tunneling charge e* ≈ e/3 for all FQH states and e* ≈ e for IQH states. Temperature decay of the oscillations appears exponential, qualitatively consistent with a recent prediction, and the surprising filling-factor dependence of the associated energy scale may shed light on edge structure.
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66
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Paradiso N, Heun S, Roddaro S, Sorba L, Beltram F, Biasiol G, Pfeiffer LN, West KW. Imaging fractional incompressible stripes in integer quantum Hall systems. PHYSICAL REVIEW LETTERS 2012; 108:246801. [PMID: 23004306 DOI: 10.1103/physrevlett.108.246801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Indexed: 06/01/2023]
Abstract
Transport experiments provide conflicting evidence on the possible existence of fractional order within integer quantum Hall systems. In fact, integer edge states sometimes behave as monolithic objects with no inner structure, while other experiments clearly highlight the role of fractional substructures. Recently developed low-temperature scanning probe techniques offer today an opportunity for a deeper-than-ever investigation of spatial features of such edge systems. Here we use scanning-gate microscopy and demonstrate that fractional features were unambiguously observed in every integer quantum Hall constriction studied. We present also an experimental estimate of the width of the fractional incompressible stripes corresponding to filling factors 1/3, 2/5, 3/5, and 2/3. Our results compare well with predictions of the edge-reconstruction theory.
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67
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Pan W, Baldwin KW, West KW, Pfeiffer LN, Tsui DC. Spin transition in the ν=8/3 fractional quantum Hall effect. PHYSICAL REVIEW LETTERS 2012; 108:216804. [PMID: 23003291 DOI: 10.1103/physrevlett.108.216804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Indexed: 06/01/2023]
Abstract
We present here the results from a density dependent study of the activation energy gaps of the fractional quantum Hall effect states at Landau level fillings ν=8/3 and 7/3 in a series of high quality quantum wells. In the density range from 0.5×10(11) to 3×10(11) cm(-2), the 7/3 energy gap increases monotonically with increasing density, supporting its ground state being spin polarized. For the 8/3 state, however, its energy gap first decreases with increasing density, almost vanishes at n~0.8×10(11) cm(-2), and then turns around and increases with increasing density, clearly demonstrating a spin transition.
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68
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Liu G, Zhang C, Tsui DC, Knez I, Levine A, Du RR, Pfeiffer LN, West KW. Enhancement of the ν = 5/2 fractional quantum Hall state in a small in-plane magnetic field. PHYSICAL REVIEW LETTERS 2012; 108:196805. [PMID: 23003074 DOI: 10.1103/physrevlett.108.196805] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Indexed: 06/01/2023]
Abstract
Using a 50-nm-width ultraclean GaAs/AlGaAs quantum well, we have studied the Landau level filling factor ν=5/2 fractional quantum Hall effect in a perpendicular magnetic field B∼1.7 T and determined its dependence on tilted magnetic fields. Contrary to all previous results, the 5/2 resistance minimum and the Hall plateau are found to strengthen continuously under an increasing tilt angle 0<θ<25° (corresponding to an in-plane magnetic field 0<B(∥)<0.8 T). In the same range of θ, the activation gaps of both the 7/3 and the 8/3 states are found to increase with tilt. The 5/2 state transforms into a compressible Fermi liquid upon tilt angle θ>60°, and the composite fermion series [2+p/(2p±1), p=1,2] can be identified. Based on our results, we discuss the relevance of a Skyrmion spin texture at ν=5/2 associated with small Zeeman energy in wide quantum wells, as proposed by Wójs et al. [Phys. Rev. Lett. 104, 086801 (2010)].
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69
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Qiu RLJ, Gao XPA, Pfeiffer LN, West KW. Connecting the reentrant insulating phase and the zero-field metal-insulator transition in a 2D hole system. PHYSICAL REVIEW LETTERS 2012; 108:106404. [PMID: 22463433 DOI: 10.1103/physrevlett.108.106404] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Indexed: 05/31/2023]
Abstract
We present the transport and capacitance measurements of 10 nm wide GaAs quantum wells with hole densities around the critical point of the 2D metal-insulator transition (critical density p(c) down to 0.8 × 10(10)/cm2, r(s) ∼ 36). For metallic hole density p(c) < p < p(c) + 0.15 × 10(10)/cm2, a reentrant insulating phase (RIP) is observed between the ν = 1 quantum Hall state and the zero-field metallic state and it is attributed to the formation of pinned Wigner crystal. Through studying the evolution of the RIP versus 2D hole density, we show that the RIP is incompressible and continuously connected to the zero-field insulator, suggesting a similar origin for these two phases.
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70
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Deng N, Kumar A, Manfra MJ, Pfeiffer LN, West KW, Csáthy GA. Collective nature of the reentrant integer quantum Hall states in the second Landau level. PHYSICAL REVIEW LETTERS 2012; 108:086803. [PMID: 22463555 DOI: 10.1103/physrevlett.108.086803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2011] [Indexed: 05/31/2023]
Abstract
We report an unexpected sharp peak in the temperature dependence of the magnetoresistance of the reentrant integer quantum Hall states in the second Landau level. This peak defines the onset temperature of these states. We find that in different spin branches the onset temperatures of the reentrant states scale with the Coulomb energy. This scaling provides direct evidence that Coulomb interactions play an important role in the formation of these reentrant states evincing their collective nature.
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71
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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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72
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Liu Y, Kamburov D, Shayegan M, Pfeiffer LN, West KW, Baldwin KW. Anomalous robustness of the ν=5/2 fractional quantum Hall state near a sharp phase boundary. PHYSICAL REVIEW LETTERS 2011; 107:176805. [PMID: 22107557 DOI: 10.1103/physrevlett.107.176805] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Indexed: 05/31/2023]
Abstract
We report magnetotransport measurements in wide GaAs quantum wells with a tunable density to probe the stability of the fractional quantum Hall effect at a filling factor of ν=5/2 in the vicinity of the crossing between Landau levels (LLs) belonging to the different (symmetric and antisymmetric) electric subbands. When the Fermi energy (E(F)) lies in the excited-state LL of the symmetric subband, the 5/2 quantum Hall state is surprisingly stable and gets even stronger near this crossing, and then suddenly disappears and turns into a metallic state once E(F) moves to the ground-state LL of the antisymmetric subband. The sharpness of this disappearance suggests a first-order transition.
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73
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Graninger AL, Kamburov D, Shayegan M, Pfeiffer LN, West KW, Baldwin KW, Winkler R. Reentrant ν=1 quantum Hall state in a two-dimensional hole system. PHYSICAL REVIEW LETTERS 2011; 107:176810. [PMID: 22107562 DOI: 10.1103/physrevlett.107.176810] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Indexed: 05/31/2023]
Abstract
We report the observation of a reentrant quantum Hall state at the Landau level filling factor ν=1 in a two-dimensional hole system confined to a 35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by a weakening and eventual collapse of the ν=1 quantum Hall state in the presence of a parallel magnetic field component B(∥), followed by a strengthening and reemergence as B(∥) is further increased. The robustness of the ν=1 quantum Hall state during the transition depends strongly on the charge distribution symmetry of the quantum well, while the magnitude of B(∥) needed to invoke the transition increases with the total density of the system.
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74
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Zhou X, Schmidt B, Proust C, Gervais G, Pfeiffer LN, West KW, Sarma SD. Quantum-classical crossover and apparent metal-insulator transition in a weakly interacting 2D Fermi liquid. PHYSICAL REVIEW LETTERS 2011; 107:086804. [PMID: 21929191 DOI: 10.1103/physrevlett.107.086804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2011] [Indexed: 05/31/2023]
Abstract
We report the observation of an apparent parallel magnetic-field-induced metal-insulator transition in a high-mobility two-dimensional electron gas for which spin and localization physics most likely play no major role. The high-mobility metallic phase at low field is consistent with the established Fermi liquid transport theory including phonon scattering, whereas the phase at higher field shows a large insulatinglike negative temperature dependence at resistances much smaller than the quantum of resistance h/e(2). We argue that this observation is a direct manifestation of a quantum-classical crossover arising predominantly from the magneto-orbital coupling between the finite width of the two-dimensional electron gas and the in-plane magnetic field.
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75
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Wurstbauer U, Majumder D, Mandal SS, Dujovne I, Rhone TD, Dennis BS, Rigosi AF, Jain JK, Pinczuk A, West KW, Pfeiffer LN. Observation of nonconventional spin waves in composite-fermion ferromagnets. PHYSICAL REVIEW LETTERS 2011; 107:066804. [PMID: 21902358 DOI: 10.1103/physrevlett.107.066804] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Indexed: 05/31/2023]
Abstract
We find unexpected low energy excitations of fully spin-polarized composite-fermion ferromagnets in the fractional quantum Hall liquid, resulting from a complex interplay between a topological order manifesting through new energy levels and a magnetic order due to spin polarization. The lowest energy modes, which involve spin reversal, are remarkable in displaying unconventional negative dispersion at small momenta followed by a deep roton minimum at larger momenta. This behavior results from a nontrivial mixing of spin-wave and spin-flip modes creating a spin-flip excitonic state of composite-fermion particle-hole pairs. The striking properties of spin-flip excitons imply highly tunable mode couplings that enable fine control of topological states of itinerant two-dimensional ferromagnets.
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