Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A42: Integer Quantum Hall Effect |
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Sponsoring Units: FIAP Chair: James Tse, University of Texas Room: Hilton Baltimore Holiday Ballroom 3 |
Monday, March 18, 2013 8:00AM - 8:12AM |
A42.00001: Study of the correlation between microwave reflection and microwave-induced magnetoresistance oscillations in the GaAs/AlGaAs two dimensional electron system Tianyu Ye, R.G. Mani, W. Wegscheider High frequency microwave illumination produces oscillatory magneto-resistance in the high mobility two dimensional electron systems (2DES) at liquid helium temperatures, in a perpendicular magnetic field. Present theories for this phenomenon include the displacement model and the inelastic model, which have hardly perfectly simulated- or predicted- experimental results such as, for example, the linear microwave polarization dependence of this effect [1]. Besides the usual direct electrical measurement on the 2DES samples, we have examined the microwave reflection to remotely sense the electron-transport in the 2DES, in order to better understand the physical contributions. Here, we compare the concurrently observed direct transport and remotely sensed reflection from the high mobility GaAs/AlGaAs samples under various microwave illumination conditions. Correlated changes between the two types of measurements are reported.\\[4pt] [1] R. G. Mani et al., Phys. Rev. B 84, 085308 (2011); A. N. Ramanayaka et al., Phys. Rev. B 85, 205315 (2012); and references therein. [Preview Abstract] |
Monday, March 18, 2013 8:12AM - 8:24AM |
A42.00002: Study of the phase-shift in the linear-polarization-angle-dependence of the microwave radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs system Han-Chun Liu, Tianyu Ye, R. G. Mani, W. Wegscheider Microwave- and terahertz-induced magneto-resistance oscillations (MTIMRO) in the two-dimensional electron system have been a topic of interest since the observation of photo-excited zero-resistance states in the GaAs/AlGaAs system. Some theoretical developments in this area have been based on the premise of linear-polarization-insensitivity of MTIMRO. Recent studies using new experimental methods have shown, however, a strong linear polarization sensitivity of MTIMRO.[1,2] In addition, Ramanayaka \textit{et al.}[2] have observed that the phase shift $\theta_{0}$, which is a parameter in a fitting formula to sinusoidal variation of diagonal resistance, R$_{\mathrm{xx}}$, with polarization angle, $\theta $, as R$_{\mathrm{xx}}(\theta )=$A$\pm $Ccos$^{\mathrm{2}}(\theta $-$\theta_{0})$, depends upon radiation frequency $f$, magnetic field $B$, and sign of $B$.[2] Here, we investigate the dependence of the phase shift $\theta_{0}$ in the linear-polarization-angle-dependence upon the above-mentioned experimental variables. In particular, we examine the relationship between $f$ and $\theta _{0}$. The results will be compared with theory.[3,4] [1] R. G. Mani \textit{et al.}, Phys. Rev. B 84, 085308 (2011). [2] A. N. Ramanayaka \textit{et al.}, Phys. Rev. B 85, 205315 (2012). [3] J. Inarrea, Appl. Phys. Lett. 100, 242103 (2012). [4] X. L. Lei and S. Y. Liu, Phys. Rev. B 86, 205303 (2012). Work has been supported by DOE DE-SC0001762. [Preview Abstract] |
Monday, March 18, 2013 8:24AM - 8:36AM |
A42.00003: Nonlinear conductance of highly mobile 2D electrons in Corbino geometry Sean Byrnes, Scott Dietrich, Sergey Vitkalov, D. V. Dmitriev, I. V Marchishin, A. A. Bykov Current induced oscillations of differential conductivity of two-dimension electrons, placed in quantizing magnetic fields, are observed in GaAs quantum wells in Corbino geometry. The conductance oscillations are described by Zener tunneling between Landau orbits in the absence of the Hall electric field[1]. An electronic state with zero-differential conductance is found in nonlinear response to an electric field E applied to two dimensional Corbino discs of highly mobile carriers. The state occurs above a critical electric field $E>E_{th} $ at low temperatures and is accompanied by an abrupt dip in the differential conductance. The proposed model consider local instability of the electric field E as the origin of the observed phenomenon. [1] A.A Bykov, D.V. Dmitriev, I.V.Marchishin, S.Byrnes, S.A.Vitkalov, Appl. Phys. Lett.$\mbox{100}$, 251602 (2012) [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 8:48AM |
A42.00004: Quantum oscillations of nonlinear response in electron systems with variable density Scott Dietrich, Sean Byrnes, Sergey Vitkalov, D.V. Dmitriev, A.V. Goran, A.A. Bykov Oscillations of dissipative resistance of two-dimensional electrons in GaAs quantum wells are observed in response to an electric current and a strong magnetic field applied perpendicular to the two-dimensional systems. The period of the current-induced oscillations does not depend on the magnetic field and temperature. At a fixed current the oscillations are periodic in inverse magnetic fields with a period that does not depend on dc bias. Oscillations were also studied in GaAs quantum wells with variable two dimensional electron density. At a fixed magnetic field the period of the current induced oscillations depends linearly on the electron density. Both results corroborate the recently proposed model that considers the DC bias-induced spatial re-population of Landau levels as the origin of the resistance oscillations. [Preview Abstract] |
Monday, March 18, 2013 8:48AM - 9:00AM |
A42.00005: Inter-subband resistance oscillations in crossed electric and magnetic fields Sergey Vitkalov, Scott Dietrich, Sean Byrnes, A.V. Goran, A.A. Bykov Quantum oscillations of nonlinear resistance are investigated in response to electric current and magnetic field applied perpendicular to single GaAs quantum wells with two populated sub-bands. At small magnetic fields current-induced oscillations appear as Landau-Zener transitions between Landau levels inside the lowest sub-band. The period of these oscillations is proportional to the magnetic field. At high magnetic fields, a different kind of quantum oscillations emerges with a period that is independent of the magnetic field. At a fixed current the oscillations are periodic in inverse magnetic field with a period that is independent of the dc bias. The proposed model considers these oscillations as a result of spatial variations of the energy separation between two sub-bands induced by the electric current (Scott Dietrich, Sean Byrnes, Sergey Vitkalov, A. V. Goran, and A. A. Bykov Phys. Rev. B~86, 075471). [Preview Abstract] |
Monday, March 18, 2013 9:00AM - 9:12AM |
A42.00006: Nonlinear transport in two-dimensional electron systems with separated Landau levels Maxim Khodas, Michael Zudov, Loren Pfeiffer, Kenneth West The resistivity of a high mobility two-dimensional electron gas subject to a weak perpendicular magnetic field and low temperatures is strongly non-linear. This nonlinearity becomes more pronounced when the Landau level width becomes smaller than the cyclotron energy; at very small dc electric fields the differential resistivity becomes strongly suppressed and can even approach zero. Using the quantum kinetics approach we calculate the characteristic current responsible for the suppression and compare the results to the experimental data obtained in a high mobility 2DES at low temperatures. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:24AM |
A42.00007: Microwave-induced resistance oscillations at low temperatures Peter Martin, Michael Zudov, John Watson, Michael Manfra, John Reno, Loren Pfeiffer, Kenneth West At low temperatures, the amplitude of microwave-induced resistance oscillations in two dimensional electron systems is predicted to scale as $1/T^2$. In contrast to this prediction, our experiments shows that the amplitude tends to saturate at low temperatures, even in the regime of very low microwave intensities. In this talk we will discuss radiation-induced heating as a possible source of the observed saturation and ways to estimate actual temperature of irradiated 2D electrons. [Preview Abstract] |
Monday, March 18, 2013 9:24AM - 9:36AM |
A42.00008: Anomalies in nonlinear transport of two-dimensional electron gas Quentin Ebner, Michael Zudov, Loren Pfeiffer, Kenneth West When a dc current is passed through a high-mobility two-dimensional electron system subject to a weak magnetic field, its differential resistivity exhibits periodic oscillations as a function of applied current. The waveform of these oscillations, known as Hall field-induced resistance oscillations, is well established both experimentally and theoretically. In this talk we will present experimental data which show dramatic deviations of the oscillation waveform from the theoretically predicted. [Preview Abstract] |
Monday, March 18, 2013 9:36AM - 9:48AM |
A42.00009: Microwave-induced resistance oscillations in tilted magnetic fields Alex Bogan, Sergei Studenikin, Andy Sachrajda, Anthony Hatke, Michael Zudov, Loren Pfeiffer, Kenneth West We have studied the effect of an in-plane magnetic field on microwave-induced resistance oscillations in a high mobility two-dimensional electron system. We have found that the oscillation amplitude decays exponentially with an in-plane component of the magnetic field. While these findings cannot be accounted for by existing theories, our analysis suggests that the decay can be explained by a quadratic-in-parallel-field correction to the quantum scattering rate. [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:00AM |
A42.00010: Effective mass from microwave photoresistance in high-mobility 2D electron systems Michael Zudov, Anthony Hatke, John Watson, Michael Manfra, Loren Pfeiffer, Kenneth West We have performed microwave photoresistance measurements in high mobility GaAs/AlGaAs quantum wells and investigated the value of the effective mass. Surprisingly, the effective mass, obtained from the period of microwave-induced resistance oscillations, is found to be considerably lower than the band mass in GaAs. This finding provides evidence for electron-electron interactions which can be probed by microwave photoresistance in very high Landau levels. In contrast, the measured magneto-plasmon dispersion revealed an effective mass which is close to the band mass, in accord with previous studies. [Preview Abstract] |
Monday, March 18, 2013 10:00AM - 10:12AM |
A42.00011: Pinning modes of solid phases in wide quantum wells near $\nu =$ 1 Anthony Hatke, Brenden Magill, Yang Liu, Lloyd Engel, Mansour Shayegan, Loren Pfeiffer, Ken West, Kurt Baldwin Near filling factor $\nu =$ 1 the microwave spectra of sufficiently low disorder two-dimensional electron systems (2DESs) exhibit a resonance [1], understood as a Wigner solid pinning mode, in which quasiparticles or quasiholes oscillate about their pinned positions. For 2DESs in a wide quantum well of thickness 54 nm and density n$=$2.4 x 10$^{\mathrm{11}}$ cm$^{\mathrm{-2}}$, we find that the resonance frequency, f$_{\mathrm{pk}}$, is comparatively enhanced for $\nu $\textless 0.88, and interpret this as a phase transition between Wigner solids, as shown by the reentrant integer quantum Hall effect (RIQHE) recently observed in wide wells under similar conditions [2]. As n is increased by gating, the transition to enhanced f$_{\mathrm{pk}}$ moves closer to $\nu =$ 1, similar to the RIQHE in [2]. [1] Chen et al., Phys. Rev. Lett. \textbf{91},016801 (2003). [2] Liu et al., Phys. Rev. Lett. \textbf{109}, 036801 (2012). [Preview Abstract] |
Monday, March 18, 2013 10:12AM - 10:24AM |
A42.00012: Effects of short-ranged disorder on pinning modes of 2D electron system near $\nu =$1 B.H. Moon, B.A. Magill, L.W. Engel, D.C. Tsui, L.N. Pfeiffer, K.W. West We performed microwave measurements on 2-D electron systems (2DES) in heterostructures of Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$As/ Al$_{0.3}$Ga$_{0.7}$As in which the 2DES resides in dilute Al alloy, with x$=$0.21, 0.33 and 0.85{\%}. The dilute Al atoms are randomly distributed [1]. Around Landau filling $\nu =$1,the samples exhibit microwave resonances which differ from pinning mode resonances observed [2] near $\nu =$1 in unalloyed samples. The alloyed samples have larger resonance frequencies, and resonances that exist over wider ranges of $\nu $, extending to \textbar $\nu $-1\textbar $\sim$ 0.2. Also in the disordered samples, the resonances are not quasiparticle-quasihole symmetric around $\nu =$1, and there is strong frequency and $\nu $ dependence in the spectra away from rational fractional $\nu $, down to 0.6. \\[4pt] [1] W. Li \textit{et al.}, \textit{Appl.Phys. Lett. }\textbf{83}, 2832 (2003).\\[0pt] [2] Y. P. Chen et al., Phys. Rev. Lett. \textbf{91},016801 (2003). [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 10:36AM |
A42.00013: Probing the lowest Landau level energy of the light hole subband in wide quantum wells Sukret Hasdemir, Yang Liu, Mansour Shayegan, Roland Winkler, Loren Pfeiffer, Ken West, Kirk Baldwin In two-dimensional hole systems (2DHSs) with finite thickness, the degeneracies of the heavy hole (HH) and light hole (LH) states are lifted. The HH-LH anti-crossing and mixing lead to non-parabolic 2D dispersion relations, especially for the LH subbands, invalidating the simple effective-mass approximation for 2DHSs. We study the magneto-resistance of 2DHSs confined to symmetric, wide GaAs quantum wells, where the second subband (LH1) is occupied. From the magnetic field ($B$) and densities where the lowest Landau level of the LH1 subband crosses the Landau levels of HH1 subband, we can extrapolate the cyclotron energy of the LH1 subband, which decreases with increasing $B$ at low fields, and increases at high field. This peculiar behavior reveals that the cyclotron mass for the LH1 subband is negative at small magnetic fields, but becomes positive at high magnetic field, consistent with theoretical simulations. [Preview Abstract] |
Monday, March 18, 2013 10:36AM - 10:48AM |
A42.00014: Determining the Location of Charged Background Impurities in High Mobility AlGaAs/GaAs 2DEG Structures Jerry Lee, Kirk Baldwin, Ken West, Loren Pfeiffer The two main Coulomb scattering contributions to the scattering rate 1/$\tau $ in the modulation-doped AlGaAs/GaAs two-dimensional electron gas (2DEG) system are scattering from unintentional background charged impurities present in the GaAs and AlGaAs materials, and scattering by the intentional dopants in the doped layer. Theoretical studies [1] indicate that for structures dominated by scattering from unintentional background charged impurities in the conducting channel, a carrier mobility $\mu $ versus 2DEG density n relationship of $\mu \approx $ n$^{\mathrm{0.8}}$ is anticipated. On the other hand, in structures where the dominant scattering mechanism is due to charged impurities or dopants in the nearby AlGaAs barriers, a relationship of $\mu \approx $ n$^{\mathrm{1.8}}$ is expected. Using high-mobility heterostructure insulated-gate field-effect transistors (HIGFETs) fabricated by molecular beam epitaxy (MBE) and lithography, we demonstrate a technique for determining the location of the mobility limiting charged impurities. We intentionally introduce charged impurities into either the barrier or the quantum well of our HIGFETs and measure the slope of $\mu $ versus n. We find a dependence of $\mu \approx $ n$^{\mathrm{0.7}}$ when the dopants are inserted into the quantum well. In contrast, we measure a dependence of $\mu \approx $ n$^{\mathrm{1.8}}$ when impurities are introduced into the barrier. Our results are in excellent agreement with theoretical predictions and pave the way towards utilizing these relationships to diagnose the exact location of impurities in high-mobility structures for FQHE applications. [1] A. Gold, Appl. Phys. Lett. \textbf{54}, 2100 (1989). [Preview Abstract] |
Monday, March 18, 2013 10:48AM - 11:00AM |
A42.00015: Monitoring Excitations of the N$=$1 Landau Level by Optical Emission at mK Temperatures Antonio Levy, Ursula Wurstbauer, Dov Fields, Aron Pinczuk, John Watson, Sumit Mondal, Michael J. Manfra, Ken W. West, Loren N. Pfeiffer Optical emission experiments have proven to be powerful contactless probe of collective states of electrons in the second (N$=$1) Landau Level (LL) [1,2]. We report the emission spectrum from optical recombination in the N$=$0 and N$=$1 LL's the second LL. The 2DEG is confined in ultra-high-mobility GaAs quantum well structures. Optical emission red-shifted from the main luminescence of the N$=$0 and N$=$1 LL are interpreted as shakeup processes of quasiparticles in the N$=$1 LL. Results of two samples with different carrier densities measured in the temperature range of 42mK$\le $T$\le $650mK will be compared. The experimental observations will be discussed taking into account the striking quantum phases dominating the second LL. [1] Manfra, M. J. et al. Phys. Rev. B 57, R9467 (1998) [2] Gravier, L. et al. Phys. Rev. Lett. 80, 3344 (1998). [Preview Abstract] |
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