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Spontaneous spin polarization in quantum point contactsSep 16 2005Apr 05 2006We use spatial spin separation by a magnetic focusing technique to probe the polarization of quantum point contacts. The point contacts are fabricated from p-type GaAs/AlGaAs heterostructures. A finite polarization is measured in the low-density regime, ... More

Alternation and interchange of e/4 and e/2 period interference oscillations as evidence for filling factor 5/2 non-Abelian quasiparticlesNov 02 2009Jul 02 2010It is a theoretical conjecture that 5/2 fractional quantum Hall state charge e/4 excitations may obey exotic non-Abelian statistics. In edge state interference these purported non-Abelian quasiparticles should display period e/4 Aharonov-Bohm oscillations ... More

Current Path Properties of the Transport Anisotropy at Filling Factor 9/2Sep 19 2001To establish the presence and orientation of the proposed striped phase in ultra-high mobility 2D electron systems at filling factor 9/2, current path transport properties are determined by varying the separation and allignment of current and voltage ... More

Experimental Demonstration of Fermi Surface Effects at Filling Factor 5/2Sep 19 2001Using small wavelength surface acoustic waves (SAW) on ultra-high mobility heterostructures, Fermi surface properties are detected at 5/2 filling factor at temperatures higher than those at which the quantum Hall state forms. An enhanced conductivity ... More

Measurement of filling factor 5/2 quasiparticle interference: observation of charge e/4 and e/2 period oscillationsJul 01 2008May 18 2009A standing problem in low dimensional electron systems is the nature of the 5/2 fractional quantum Hall state: its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum ... More

Simple-layered high mobility field effect heterostructured two-dimensional electron deviceMar 27 2007We present a two-dimensional electron heterostructure field effect device of simplistic design and ease of fabrication that displays high mobility electron transport. This is accomplished using a high efficacy contacting scheme and simple metallic overlapping ... More

Magnetic field induced resistance properties at filling factor 5/2 consistent with non-Abelian e/4 quasiparticles in multiple sized interferometersApr 09 2012Non-Abelian e/4 quasiparticles at 5/2 filling factor in a correlated two-dimensional electron gas have a proposed specific property in an interference measurement of their edge propagation: encircling an even number of localized e/4 quasiparticles allows ... More

Evidence for current flow anomalies in the irradiated 2D electron system at small magnetic fieldsAug 20 2003We report experimental results of low temperature magnetotransport in high mobility 2D electron systems exposed to radiation up to 20GHz frequency using a simple dipole configuration. Magnetoresistance oscillations are observed as in previously reported ... More

Evidence for A Two-dimensional Quantum Wigner Solid in Zero Magnetic FieldJun 18 2013Oct 02 2013We report the first experimental observation of a characteristic nonlinear threshold behavior from dc dynamical response as an evidence for a Wigner crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The system under increasing ... More

Precursors to Exciton Condensation in Quantum Hall BilayersMar 19 2019Tunneling spectroscopy reveals evidence for interlayer electron-hole correlations in quantum Hall bilayer two-dimensional electron systems at layer separations near, but above, the transition to the incompressible exciton condensate at total Landau level ... More

Light-induced long-ranged disorder effect in ultra-dilute two-dimensional holes in GaAs heterojunction-insulated-gate field-effect-transistorsJun 26 2013Comparing the results of transport measurements of strongly correlated two-dimensional holes in a GaAs heterojunction-insulated-gate field-effect-transistor obtained before and after a brief photo-illumination, the light-induced disorder is found to cause ... More

Effect of Nyquist Noise on the Nyquist Dephasing Rate in 2d Electron SystemsJul 23 2001Aug 21 2001We measure the effect of externally applied broadband Nyquist noise on the intrinsic Nyquist dephasing rate of electrons in a two-dimensional electron gas at low temperatures. Within the measurement error, the phase coherence time is unaffected by the ... More

Experimental evidence of low-lying gapped excitations in the quantum fluid at nu=5/2Apr 20 2012The low-lying neutral excitation spectrum of the incompressible quantum Hall fluid at $\nu=5/2$ 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 ... More

Breakdown of Particle-Hole Symmetry in the Lowest Landau Level Revealed by Tunneling SpectroscopyJul 30 2009Tunneling measurements on 2D electron gases at high magnetic field reveal a qualitative difference between the two spin sublevels of the lowest Landau level. While the tunneling current-voltage characteristic at filling factor $\nu = 1/2$ is a single ... More

Effect of in-plane magnetic field on the photoluminescence spectrum of modulation-doped quantum wells and heterojunctionsOct 05 2004The photoluminescence (PL) spectrum of modulation-doped GaAs/AlGaAs quantum wells (MDQW) and heterojunctions (HJ) is studied under a magnetic field ($B_{\|}$) applied parallel to the two-dimensional electron gas (2DEG) layer. The effect of $B_{\|}$ strongly ... More

Characteristic Sign Change of the Magnetoresistance of Strongly Correlated GaAs Two-dimensional HolesJun 27 2013High quality strongly correlated two-dimensional (2D) electron systems at low temperatures $T\rightarrow 0$ exhibits an apparent metal-to-insulator transition (MIT) at a large $r_s$ value around 40. We have measured the magnetoresistance of 2D holes in ... More

Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by Optically Pumped NMRJul 19 1999Jul 20 1999Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra provide evidence that spin-reversed ... More

Optically Pumped NMR Measurements of the Electron Spin Polarization in GaAs Quantum Wells near Landau Level Filling Factor nu=1/3Jan 20 1998Jul 20 1998The Knight shift of Ga-71 nuclei is measured in two different electron-doped multiple quantum well samples using optically pumped NMR. These data are the first direct measurements of the electron spin polarization, P(nu,T)=<Sz(nu,T)>/max<Sz>, near nu=1/3. ... More

Observation of Incompressibility at $ν=4/11$ and $ν=5/13$Dec 28 2014The region of filling factors $1/3<\nu<2/5$ is predicted to support new types of fractional quantum Hall states with topological order different from that of the Laughlin-Jain or the Moore-Read states. Incompressibility is a necessary condition for the ... More

Localization in Artificial Disorder - Two Coupled Quantum DotsJan 31 2000Using Single Electron Capacitance Spectroscopy, we study electron additions in quantum dots containing two potential minima separated by a shallow barrier. Analysis of addition spectra in magnetic field allows us to distinguish whether electrons are localized ... More

Integrated Electronic Transport and Thermometry at milliKelvin Temperatures and in Strong Magnetic FieldsMay 12 2011We fabricated a He-3 immersion cell for transport measurements of semiconductor nanostructures at ultra low temperatures and in strong magnetic fields. We have a new scheme of field-independent thermometry based on quartz tuning fork Helium-3 viscometry ... More

The Localization-Delocalization Transition in Quantum DotsDec 09 1999Single-electron capacitance spectroscopy precisely measures the energies required to add individual electrons to a quantum dot. The spatial extent of electronic wavefunctions is probed by investigating the dependence of these energies on changes in the ... More

Observation of a Transition in the $ν=5/2$ Fractional Quantum Hall State at Large Landau Level MixingFeb 06 2013We have studied the $\nu=5/2$ fractional quantum Hall state in the regime of extremely low densities, for which the Landau level mixing parameter $\kappa$ spans the so far unexplored $2.52<\kappa<2.82$ range. In the vicinity of $\kappa = 2.6$ an unexpectedly ... More

Particle-hole Asymmetry of Fractional Quantum Hall States in the Second Landau Level of a Two-dimensional Hole SystemJul 09 2010May 15 2011We report the first unambiguous observation of a fractional quantum Hall state in the Landau level of a two-dimensional hole sample at the filling factor $\nu=8/3$. We identified this state by a quantized Hall resistance and an activated temperature dependence ... More

Evidence for the Collective Nature of the Reentrant Integer Quantum Hall States of the Second Landau LevelOct 18 2011We 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 ... More

Anisotropic modification of the effective hole $g$-factor by electrostatic confinementFeb 28 2008We investigate effects of lateral confinement on spin splitting of energy levels in 2D hole gases grown on [311] GaAs. We found that lateral confinement enhances anisotropy of spin splitting relative to the 2D gas for both confining directions. Unexpectedly, ... More

Geometry dependent dephasing in small metallic wiresJun 20 2000Temperature dependent weak localization is measured in metallic nanowires in a previously unexplored size regime down to width $w=5$ nm. The dephasing time, $\tau_{\phi}$, shows a low temperature $T$ dependence close to quasi-1D theoretical expectations ... More

Magnetic field-tuned Aharonov-Bohm oscillations and evidence for non-Abelian anyons at v=5/2Jan 12 2013We show that the resistance of the v=5/2 quantum Hall state, confined to an interferometer, oscillates with magnetic field consistent with an Ising-type non-Abelian state. In three quantum Hall interferometers of different sizes, resistance oscillations ... More

Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau LevelsMar 09 2002We observe density induced 90$^{\circ}$ rotations of the anisotropy axes in transport measurements at half-filled high Landau levels in the two dimensional electron system, where stripe states are proposed ($\nu$=9/2, 11/2, etc). Using a field effect ... More

Spin Transition in the Half-Filled Landau LevelSep 24 2006Mar 26 2007The transition from partial to complete spin polarization of two-dimensional electrons at half filling of the lowest Landau level has been studied using resistively-detected nuclear magnetic resonance (RDNMR). The nuclear spin-lattice relaxation time ... More

Pinning mode resonances of 2D electron stripe phases: Effect of in-plane magnetic fieldOct 20 2008We study the anisotropic pinning-mode resonances in the rf conductivity spectra of the stripe phase of 2D electron systems (2DES) around Landau level filling 9/2, in the presence of an in-plane magnetic field, B_ip. The polarization along which the resonance ... More

Anisotropic Disorder in High Mobility 2D Heterostructures and its Correlation to Electron TransportJul 07 2000Jul 26 2000Surface morphology of high mobility heterostructures is examined and correlated with d.c. transport. {\it All} samples examined show evidence of lines in the [1$\bar{1}$0] direction with roughness ranging from small amplitude features to severe anisotropic ... More

Periodic and Aperiodic Bunching in the Addition Spectra of Quantum DotMar 27 1997We study electron addition spectra of quantum dots in a broad range of electron occupancies starting from the first electron. Spectra for dots containing <200 electrons reveal a surprising feature. Electron additions are not evenly spaced in gate voltage. ... More

Spin separation in cyclotron motionMar 26 2004Sep 28 2004Charged carriers with different spin states are spatially separated in a two-dimensional hole gas. Due to strong spin-orbit interaction holes at the Fermi energy have different momenta for two possible spin states travelling in the same direction and, ... More

Surface Acoustic Wave Propagation and Inhomogeneities in Low Density Two-Dimensional Electron Systems Near the Metal-Insulator TransitionJul 04 2005We have measured the surface acoustic wave velocity shift in a GaAs/AlGaAs heterostructure containing a two-dimensional electron system (2DES) in a low-density regime ($<$ $10^{10}$ cm$^{-2}$) at zero magnetic field. The interaction of the surface acoustic ... More

Probing the Melting of a Two-dimensional Quantum Wigner Crystal via its Screening EfficiencyMar 24 2019One of the most fundamental and yet elusive collective phases of an interacting electron system is the quantum Wigner crystal (WC), an ordered array of electrons expected to form when the electrons' Coulomb repulsion energy eclipses their kinetic (Fermi) ... More

Microwave pinning modes near Landau filling $ν=1$ in two-dimensional electron systems with alloy disorderDec 01 2014We report measurements of microwave spectra of two-dimensional electron systems hosted in dilute Al alloy, Al$_x$Ga$_{1-x}$As, for a range of Landau level fillings, $\nu$, around 1. For $\nu>0.8$ or $\nu<1.2$, the samples exhibit a microwave resonance ... More

Aharonov-Bohm effect and coherence length of charge e/4 quasiparticles at 5/2 filling factor measured in multiple small Fabry-Perot interferometersJan 11 2013Design of a Fabry-Perot (double point contact) interferometer to measure fractional quantum Hall effect quasiparticle charge properties, and in particular the 5/2 excitations, poses an important trade-off: the device size should be minimized to allow ... More

Giant negative magnetoresistance in high-mobility 2D electron systemsJan 27 2012We report on a giant negative magnetoresistance in very high mobility GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at $B \simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T \lesssim 2$ K. Unlike ... More

Anomalous spin-resolved point-contact transmission of holes due to cubic Rashba spin-orbit couplingNov 11 2010Jun 11 2011Evidence is presented for the finite wave vector crossing of the two lowest one-dimensional spin-split subbands in quantum point contacts fabricated from two-dimensional hole gases with strong spin-orbit interaction. This phenomenon offers an elegant ... More

Surface Acoustic Waves Probe of the Spin Phase Transition at $ν$=2/3 in n-GaAs/AlGaAs structureNov 20 2015High frequency (ac) conductivity in the single quantum well AlGaAs/GaAs/AlGaAs with high mobility was investigated by contactless acoustic methods in the fractional quantum Hall effect regime in perpendicular and tilted magnetic fields. We studied the ... More

Resonant Subband Landau Level Coupling in Symmetric Quantum WellJul 07 2010Subband structure and depolarization shifts in an ultra-high mobility GaAs/Al_{0.24}Ga_{0.76}As quantum well are studied using magneto-infrared spectroscopy via resonant subband Landau level coupling. Resonant couplings between the 1st and up to the 4th ... More

Influence of a Parallel Magnetic Field on Microwave Photoconductivity in a High-Mobility 2D Electron SystemApr 27 2005We have studied experimentally the influence of a parallel magnetic field ($B_{//}$) on microwave-induced resistance oscillations (MIRO) and zero-resistance states (ZRS) previously discovered in a high-mobility 2D electron system. We have observed a strong ... More

Microwave photoresistance of a high-mobility two-dimensional electron gas in a triangular antidot latticeJul 27 2006The microwave (MW) photoresistance has been measured on a high-mobility two-dimensional electron gas patterned with a shallow triangular antidot lattice, where both the MW-induced resistance oscillations (MIRO) and magnetoplasmon (MP) resonance are observed ... More

AFM local oxidation nanopatterning of a high mobility shallow 2D hole gasMar 02 2003Recently developed AFM local anodic oxidation (LAO) technique offers a convenient way of patterning nanodevices, but imposes even more stringent requirements on the underlying quantum well structure. We developed a new very shallow quantum well design ... More

Hysteresis and Spikes in the Quantum Hall EffectSep 06 1999Sep 07 1999We observe sharp peaks and strong hysteresis in the electronic transport of a two-dimensional electron gas (2DEG) in the region of the integral quantum Hall effect. The peaks decay on time scales ranging from several minutes to more than an hour. Momentary ... More

Resistively-Detected NMR in a Two-Dimensional Electron System near $ν = 1$: Clues to the Origin of the Dispersive LineshapeNov 14 2005Mar 07 2006Resistively-detected NMR measurements on 2D electron systems near the $\nu = 1$ quantum Hall state are reported. In contrast to recent results of Gervais \emph{et al.} [Phys. Rev. Lett. $\bf 94$, 196803 (2005)], a dispersive lineshape is found at all ... More

Tunneling between the Edges of Two Lateral Quantum Hall SystemsOct 14 1999The edge of a two-dimensional electron system (2DES) in a magnetic field consists of one-dimensional (1D) edge-channels that arise from the confining electric field at the edge of the specimen$^{1-3}$. The crossed electric and magnetic fields, E x B, ... More

Connecting the Reentrant Insulating Phase and the Zero Field Metal-Insulator Transition in a 2D Hole SystemSep 24 2011We present the transport and capacitance measurements of 10nm 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$\times10^{10}$/cm$^2$, $r_s\sim$36). For metallic ... More

Pinning modes of high magnetic field Wigner solids with controlled alloy disorderJan 16 2014For a series of samples with 2D electron systems in dilute Al_x Ga_{1-x}As, with varying x from 0 to 0.8 %, we survey the pinning mode resonances of Wigner solids at the low Landau filling termination of the fractional quantum Hall effect (FQHE) series. ... More

A system for measuring auto- and cross-correlation of current noise at low temperaturesApr 02 2006Jun 09 2006We describe the construction and operation of a two-channel noise detection system for measuring power and cross spectral densities of current fluctuations near 2 MHz in electronic devices at low temperatures. The system employs cryogenic amplification ... More

Mesoscopic structures and 2D hole systems in fully field effect controlled heterostructuresMar 27 2007Two fundamental extensions to the function of previously described fully field effect two-dimensional (2D) electron heterostructures are presented: First, using the same basic heterostructure design of lithographically defined contacts overlain by both ... More

Confinement of fractional quantum Hall states in narrow conducting channelsMar 08 2007Confinement of small-gapped fractional quantum Hall states facilitates quasiparticle manipulation and is an important step towards quasiparticle interference measurements. Demonstrated here is conduction through top gate defined, narrow channels in high ... More

Spin Susceptibility of an Ultra-Low Density Two Dimensional Electron SystemJan 11 2003We determine the spin susceptibility in a two dimensional electron system in GaAs/AlGaAs over a wide range of low densities from 2$\times10^{9}$cm$^{-2}$ to 4$\times10^{10}$cm$^{-2}$. Our data can be fitted to an equation that describes the density dependence ... More

Spin Transition in Strongly Correlated Bilayer Two Dimensional Electron SystemsOct 04 2004Using a combination of heat pulse and nuclear magnetic resonance techniques we demonstrate that the phase boundary separating the interlayer phase coherent quantum Hall effect at $\nu_T = 1$ in bilayer electron gases from the weakly coupled compressible ... More

Critical Filling Factor for the Formation of a Quantum Wigner Crystal Screened by a Nearby LayerAug 19 2018Aug 21 2018One of the most fascinating ground states of an interacting electron system is the so-called Wigner crystal where the electrons, in order to minimize their repulsive Coulomb energy, form an ordered array. Here we report measurements of the critical filling ... More

Non-linear response of a high mobility two-dimensional electron system near the second harmonic of the cyclotron resonanceMay 06 2011Recent experiments on microwave-irradiated high-mobility two-dimensional electron systems revealed a novel photoresistivity peak in the vicinity of the second cyclotron resonance harmonic. Here we report on the nonlinear transport measurements and demonstrate ... More

Hall field-induced resistance oscillations in tilted magnetic fieldsJan 14 2011Jan 26 2011We have studied the effect of an in-plane magnetic field on Hall field-induced resistance oscillations in high mobility two-dimensional electron systems. We have found that the oscillation frequency depends only on the perpendicular component of the magnetic ... More

Resonant Rayleigh scattering from quantum phases of cold electrons in semiconductor heterostructuresJun 12 2006Resonant Rayleigh scattering of light from electrons confined in gallium arsenide double quantum wells displays significant changes at temperatures that are below one degree Kelvin. The Rayleigh resonance occurs for photon energies that overlap a quantum ... More

Anomalous structure in the single particle spectrum of the fractional quantum Hall effectMay 21 2010The two-dimensional electron system (2DES) is a unique laboratory for the physics of interacting particles. Application of a large magnetic field produces massively degenerate quantum levels known as Landau levels. Within a Landau level the kinetic energy ... More

Dynamic Nuclear Polarization in the Fractional Quantum Hall RegimeApr 26 2010We investigate dynamic nuclear polarization in quantum point contacts (QPCs) in the integer and fractional quantum Hall regimes. Following the application of a dc bias, fractional plateaus in the QPC shift symmetrically about half filling of the lowest ... More

Resonant Phonon Scattering in Quantum Hall Systems Driven by dc Electric FieldsNov 09 2007Using dc excitation to spatially tilt Landau levels, we study resonant acoustic phonon scattering in two-dimensional electron systems. We observe that dc electric field strongly modifies phonon resonances, transforming resistance maxima into minima and ... More

Magnetic Field Induced Insulating Phases at Large $r_s$Aug 06 2004Exploring a backgated low density two-dimensional hole sample in the large $r_s$ regime we found a surprisingly rich phase diagram. At the highest densities, beside the $\nu=1/3$, 2/3, and 2/5 fractional quantum Hall states, we observe both of the previously ... More

Crossover and Coexistence of Quasiparticle Excitations in the Fractional Quantum Hall Regime at $ν\leq 1/3$Jun 05 2003New low-lying excitations are observed by inelastic light scattering at filling factors $\nu=p/(\phi p \pm 1)$ of the fractional quantum Hall regime with $\phi=4$. Coexisting with these modes throughout the range $\nu \leq 1/3$ are $\phi=2$ excitations ... More

Missing 2k_F Response for Composite Fermions in Phonon DragJul 26 1999The response of composite Fermions to large wavevector scattering has been studied through phonon drag measurements. While the response retains qualitative features of the electron system at zero magnetic field, notable discrepancies develop as the system ... More

Evidence for a $ν=5/2$ Fractional Quantum Hall Nematic State in Parallel Magnetic FieldsFeb 26 2013We report magneto-transport measurements for the fractional quantum Hall state at filling factor $\nu=$ 5/2 as a function of applied parallel magnetic field ($B_{||}$). As $B_{||}$ is increased, the 5/2 state becomes increasingly anisotropic, with the ... More

Area dependence of interlayer tunneling in strongly correlated bilayer 2D electron systems at $ν_T=1$May 15 2008The area and perimeter dependence of the Josephson-like interlayer tunneling signature of the coherent $\nu_T=1$ quantum Hall phase in bilayer two-dimensional electron systems is examined. Electrostatic top gates of various sizes and shapes are used to ... More

Observation of anti-levitation of Landau levels in vanishing magnetic fieldsApr 18 2016Apr 19 2016We report an anti-levitation behavior of Landau levels in vanishing magnetic fields in a high quality hetero-junction insulated-gated field-effect transistor. We found, in the Landau fan diagram of electron density versus magnetic field, the positions ... More

Interaction effects in the transport of two-dimensional holes in GaAsOct 11 2006The power-law increase of the conductivity with temperature in the nominally insulating regime, recently reported for the dilute two-dimensional holes [cond-mat/0603053], is found to systematically vary with the carrier density. Based on the results from ... More

Non-activated transport of strongly interacting two-dimensional holes in GaAsMar 02 2006Oct 11 2006We report on the transport measurements of two-dimensional holes in GaAs field effect transistors with record low densities down to 7*10^8 cm^{-2}. Remarkably, such a dilute system (with Fermi wavelength approaching 1 micrometer) exhibits a non-activated ... More

Evidence for a New Dissipationless Regime in 2D Electronic TransportOct 01 2002In an ultra-clean 2D electron system (2DES) subjected to crossed millimeterwave (30--150 GHz) and weak (B < 2 kG) magnetic fields, a series of apparently dissipationless states emerges as the system is detuned from cyclotron resonances. Such states are ... More

Inelastic Light Scattering by Gap Excitations of Fractional Quantum Hall States at 1/3 <= ν<= 2/3Nov 22 1999We report observations of collective gap excitations of the fractional quantum Hall (FQH) states at filling factors \nu=p/(2p+1) (p=integer), for 1/3 <= \nu <= 2/3, by inelastic light scattering. The collective gap energies at \nu= 1/3, 2/5 and 3/7 show ... More

Vertical Confinement and Evolution of Reentrant Insulating Transition in the Fractional Quantum Hall RegimeFeb 24 2003We have observed an anomalous shift of the high field reentrant insulating phases in a two-dimensional electron system (2DES) tightly confined within a narrow GaAs/AlGaAs quantum well. Instead of the well-known transitions into the high field insulating ... More

Cascade of Quantum Phase Transitions in Tunnel-Coupled Edge StatesNov 03 2003Feb 04 2004We report on the cascade of quantum phase transitions exhibited by tunnel-coupled edge states across a quantum Hall line junction. We identify a series of quantum critical points between successive strong and weak tunneling regimes in the zero-bias conductance. ... More

Reply to Simon's Comment on "Evidence for an Anisotropic State of Two-Dimensional Electrons in High Landau Levels"Mar 09 1999We recently reported [PRL 82, 394 (1999)] large transport anisotropies in a two-dimensional electron gas in high Landau levels. These observations were made utilizing both square and Hall bar sample geometries. Simon recently commented [cond-mat/9903086] ... More

Insulating and Fractional Quantum Hall States in the N=1 Landau LevelOct 22 2001The observation of new insulating phases of two-dimensional electrons in the first excited Landau level is reported. These states, which are manifested as re-entrant integer quantized Hall effects, exist alongside well-developed even-denominator fractional ... More

New collective states of 2D electrons in high Landau levelsMar 24 2000A brief summary of the emerging evidence for a new class of collective states of two-dimensional electrons in partially occupied excited Landau levels is presented. Among the most dramatic phenomena described are the large anisotropies of the resistivity ... More

Zero differential resistance in two-dimensional electron systems at large filling factorsJul 16 2010We report on a state characterized by a zero differential resistance observed in very high Landau levels of a high-mobility two-dimensional electron system. Emerging from a minimum of Hall field-induced resistance oscillations at low temperatures, this ... More

Non-linear magnetotransport in microwave-illuminated two-dimensional electron systemsApr 18 2008May 24 2008We study magnetoresistivity oscillations in a high-mobility two-dimensional electron system subject to both microwave and dc electric fields. First, we observe that the oscillation amplitude is a periodic function of the inverse magnetic field and is ... More

Resonance Magnetoresistance in Coupled Quantum WellsJun 27 1994The in-plane magnetic field suppresses the quantum coupling between electrons in a double quantum well structure. The microscopical theory of this effect is developed and confirmed experimentally. We have shown that the decrease of the "resistance resonance" ... More

Resonant Transport in Coupled Quantum Wells: a Probe for Scattering MechanismsApr 11 1994We present a microscopical theory and experimental results concerning resistance resonance in two tunneling coupled quantum wells with different mobilities. The shape of the resonance appears to be sensitive to the small angle scattering rate on remote ... More

Fractional Quantum Hall Effect in the Second Landau LevelJul 02 2007Jul 03 2007We present activation gap measurements of the fractional quantum Hall effect (FQHE) in the second Landau level. Signatures for 14 (5) distinct incompressible FQHE states are seen in a high (low) mobility sample with the enigmatic 5/2 even denominator ... More

Lifetime of Two-Dimensional Electrons Measured by Tunneling SpectroscopyJun 09 1995For electrons tunneling between parallel two-dimensional electron systems, conservation of in-plane momentum produces sharply resonant current-voltage characteristics and provides a uniquely sensitive probe of the underlying electronic spectral functions. ... More

Quantum Lifetime of Two-Dimensional HolesMay 28 2007Jul 27 2007The quantum lifetime of two-dimensional holes in a GaAs/AlGaAs double quantum well is determined via tunneling spectroscopy. At low temperatures the lifetime is limited by impurity scattering but at higher temperatures hole-hole Coulomb scattering dominates. ... More

Exciton Transport and Andreev Reflection in a Bilayer Quantum Hall SystemDec 19 2010Jun 06 2011We demonstrate that counterflowing electrical currents can move through the bulk of the excitonic quantized Hall phase found in bilayer two-dimensional electron systems (2DES) even as charged excitations cannot. These counterflowing currents are transported ... More

Quantum Hall Exciton Condensation at Full Spin PolarizationNov 12 2009Using Coulomb drag as a probe, we explore the excitonic phase transition in quantum Hall bilayers at nu=1 as a function of Zeeman energy, E_Z. The critical layer separation d/l for exciton condensation initially increases rapidly with E_Z, but then reaches ... More

Current-induced nuclear-spin activation in a two-dimensional electron gasApr 22 2009Electrically detected nuclear magnetic resonance was studied in detail in a two-dimensional electron gas as a function of current bias and temperature. We show that applying a relatively modest dc-current bias, I_dc ~ 0.5 microAmps, can induce a re-entrant ... More

High Resolution Spectroscopy of Two-Dimensional Electron SystemsJul 11 2007Spectroscopic methods involving the sudden injection or ejection of electrons in materials are a powerful probe of electronic structure and interactions. These techniques, such as photoemission and tunneling, yield measurements of the "single particle" ... More

Magnetoresistance Oscillations in Two-dimensional Electron Systems Induced by AC and DC FieldsJan 29 2007We report on magnetotransport measurements in a high-mobility two-dimentional electron system subject simultaneously to AC (microwave) and DC (Hall) fields. We find that DC excitation affects microwave photoresistance in a nontrivial way. Photoresistance ... More

Double layer two-dimensional electron systems: Probing the transition from weak to strong coupling with Coulomb dragNov 22 2002Frictional drag measurements revealing anomalously large dissipation at the transition between the weakly- and strongly-coupled regimes of a bilayer two-dimensional electron system at total Landau level filling factor $\nu_T =1$ are reported. This result ... More

Evidence for Skyrmions and Single Spin Flips in the Integer Quantized Hall EffectJun 28 1995We have employed tilted-field magneto-transport measurements of the energy gap for the odd-integer quantized Hall states at Landau level filling factors $\nu = 1$,3 and 5 to determine the spin of thermally excited quasielectron-quasihole pairs. At $\nu ... More

Multiphoton microwave photoresistance in a high-mobility two-dimensional electron gasDec 20 2011We report on experimental and theoretical studies of microwave-induced resistance oscillations in a two-dimensional electron gas over a wide range of microwave intensities. We observe a distinct crossover from linear to sublinear power dependence of the ... More

Observations of Plasmarons in a System of Massive ElectronsSep 02 2010Calculations of the single particle density of states (SPDOS) of electron liquids have long predicted that there exist two distinct charged excitations: the usual quasiparticle consisting of an electron or hole screened by a correlation hole, and a "plasmaron" ... More

Fermi liquid to Luttinger liquid transition at the edge of a two-dimensional electron gasApr 30 2001We present experimental results on the tunneling into the edge of a two dimensional electron gas (2DEG) obtained with a GaAs/AlGaAs cleaved edge overgrown structure in a strong perpendicular magnetic field. While the 2DEG exhibits typical fractional quantum ... More

Observation of a Linearly Dispersing Collective Mode in a Quantum Hall FerromagnetDec 06 2000May 30 2001Double layer two-dimensional electron systems can exhibit a fascinating collective phase believed to exhibit both quantum ferromagnetism and excitonic superfluidity. This unusual phase has recently been found to exhibit tunneling phenomena reminiscent ... More

Coulomb Drag in the Extreme Quantum LimitOct 03 1997Coulomb drag resulting from interlayer electron-electron scattering in double layer 2D electron systems at high magnetic field has been measured. Within the lowest Landau level the observed drag resistance exceeds its zero magnetic value by factors of ... More

Observation of An Anisotropic Wigner CrystalJan 26 2016We report a new correlated phase of two-dimensional charged carriers in high magnetic fields, manifested by an anisotropic insulating behavior at low temperatures. It appears near Landau level filling factor $\nu=1/2$ in hole systems confined to wide ... More

Phase Diagrams for the $ν$ = 1/2 Fractional Quantum Hall Effect in Electron Systems Confined to Symmetric, Wide GaAs Quantum WellsJun 22 2013Nov 29 2013We report an experimental investigation of fractional quantum Hall effect (FQHE) at the even-denominator Landau level filling factor $\nu$ = 1/2 in very high quality wide GaAs quantum wells, and at very high magnetic fields up to 45 T. The quasi-two-dimensional ... More

Hole-flux Composite Fermion Commensurability OscillationsAug 03 2012We report the observation of commensurability oscillations of hole-flux composite fermions near filling factor $\nu=1/2$ in a high-mobility two-dimensional hole system confined to a GaAs quantum well, and subjected to a weak, strain-induced, unidirectional ... More

Evidence for a finite temperature phase transition in a bilayer quantum Hall systemSep 05 2007Jan 25 2008We study the Josephson-like interlayer tunneling signature of the strongly correlated $\nu_T = 1$ quantum Hall phase in bilayer two-dimensional electron systems as a function of the layer separation, temperature and interlayer charge imbalance. Our results ... More