Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G5: Integer Quantum Hall Effects |
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Sponsoring Units: FIAP Chair: Ramesh Mani, Georgia State University Room: Juan Gorman Room 005 |
Tuesday, March 3, 2015 11:15AM - 11:27AM |
G5.00001: Mach-Zehnder interferometry with periodic voltage pulses Patrick Hofer, Christian Flindt We investigate theoretically a Mach-Zehnder interferometer driven by periodic voltage pulses. We illustrate how the electronic energy distribution of the driven contact influences the visibilities of the Aharonov-Bohm oscillations in the current and in the noise. For the current, the visibility factorizes in analogy to the static case and we find a universality at path-length differences equal to multiples of the spacing between the voltage pulses. In the noise oscillations, we find additional features which are characteristic to time-dependent transport. Finite electronic temperatures are found to have a qualitatively different influence on the current and the noise. [Preview Abstract] |
Tuesday, March 3, 2015 11:27AM - 11:39AM |
G5.00002: Evolution of the linear-polarization-angle-dependence of the radiation-induced magnetoresistance-oscillations with the microwave power Tianyu Ye, Ramesh Mani, Werner Wegscheider Microwave radiation-induced magnetoresistance oscillations (MRIMRO) are huge photo-excited oscillations in the resistance in a transverse magnetic field, which are sensitive to different aspects of the microwave radiation such as the microwave frequency, microwave power, and linear polarization angle. As a consequence, MRIMROs are potentially interesting for sensing applications. In order to better understand the role of the microwave power and the linear polarization angle in MRIMROs, the role of these variables have been more carefully examined in this experimental study. Thus, the diagonal resistance $R_{xx}$ was measured as a function of both the microwave power ($P)$ and the linear polarization angle ($\theta )$ at the MRIMRO extrema. Color contour plots reveal that $R_{xx}$ vs $\theta $ follows a cosine square function at relatively low microwave power with systematic lineshape distortions occurring with increasing microwave power. Here, we demonstrate that the non-linearity of $R_{xx} $vs $P$ relation is the main factor that influences the lineshape distortion from the sinusoidal $R_{xx}$ vs $\theta $ relation observed at low $P$. [Preview Abstract] |
Tuesday, March 3, 2015 11:39AM - 11:51AM |
G5.00003: Tunneling spectroscopic evidence of quasiparticle crystallization near $v=1$ quantum Hall ferromagnet Joonho Jang, Benjamin Hunt, Raymond Ashoori, Loren Pfeiffer, Ken West We have used Time Domain Capacitance Spectroscopy to measure the density of states of 2 dimensional holes in Carbon doped GaAs at temperature of 20 mK and high magnetic fields. Filling factor dependent anomalous features, which is antisymmetric in energy and density, were observed around the quantum Hall ferromagnet $v=1$. The analysis of the quasiparticle dynamics around $v=1$ is consistent with the picture that holes are dressed by interactions with bosonic degrees of freedom. We attribute this bosonic mode to the gapless Goldstone mode emergent due to the development of crystalline order of charged quasiparticles. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:03PM |
G5.00004: Dynamics of Quantal Heating in Electron Systems with Discrete Spectra William Mayer, Scott Dietrich, Sergey Vitkalov, Alexey Bykov The temporal evolution of quantal Joule heating of 2D electrons in GaAs quantum well placed in quantizing magnetic fields is studied using a difference frequency method. The method is based on measurements of the electron conductivity oscillating at the beat frequency $f=f_1-f_2$ between two microwaves applied to 2D system at frequencies $f_1$ and $f_2$. The method provides $direct$ access to the dynamical characteristics of the heating and yields the inelastic scattering time $\tau_{in}$ of 2D electrons. The obtained $\tau_{in}$ is strongly temperature dependent, varying from 0.13 ns at 5.5K to 1 ns at 2.4K in magnetic field $B$=0.333T. When temperature $T$ exceeds the Landau level separation the relaxation rate $1/\tau_{in}$ is proportional to $T^2$, indicating the electron-electron interaction as the dominant mechanism limiting the quantal heating. At lower temperatures the rate tends to be proportional to $T^3$, indicating considerable contribution from electron-phonon scattering.\\ This work was supported by the National Science Foundation (DMR 1104503), the Russian Foundation for Basic Research (project no.14-02-01158) and the Ministry of Education and Science of the Russian Federation. [Preview Abstract] |
Tuesday, March 3, 2015 12:03PM - 12:15PM |
G5.00005: The Quantum Hall Effect with electron-boson interaction is not exact Karin Everschor-Sitte, Matthias Sitte, Allan MacDonald The quantum Hall effect (QHE) normally refers to quantized Hall conductivity due to Landau quantization, as observed in 2D electron systems. The precision of the QHE which occurs near integer Landau level filling factors has been verified to more than 8 figures. There are no known limitations to the accuracy of the QHE in the limit of zero temperature. Here, we show explicitly within a toy model that electron-boson interactions can sometimes lead to corrections to the exact quantization of the Hall conductivity. This is in particular relevant for the QAHE, which has been realized experimentally in topological insulators in 2013 [1]. In these systems interactions between surface-state electrons and magnons provide a possible mechanism for corrections to the quantum Hall effect.\\[.2em] \noindent [1] C. Chang \textit{et al.}, Science \textbf{340}, 167--170 (2013). [Preview Abstract] |
Tuesday, March 3, 2015 12:15PM - 12:27PM |
G5.00006: Intersubband Oscillations in GaAs Quantum Wells with Three Populated Subbands Jesse Kanter, Scott Dietrich, William Mayer, Sergey Vitkalov, Alexey Bykov The magnetotransport of highly mobile 2D electrons is studied in GaAs quantum wells with three occupied subbands. The lower two subbands have nearly the same energy while the third subband has a much higher energy ($E_1 \approx E_2 << E_3$). Observed magneto-intersubband oscillations (MISO) obey the relation $\Delta_{ij}=(E_i-E_j)=k\cdot\hbar\omega_c$ for oscillations between the $i^{th}$ and $j^{th}$ bands where $\omega_c$ is the cyclotron frequency and $k$ is an integer. The slight difference in the energies of the lower subbands produces noticeable interference effects in the magnetoresistance. By analyzing the amplitude of each component of the MISOs separately, the temperature dependence of the quantum lifetime $\tau_q^{(i)}$ of electrons in $i^{th}$ subband is extracted. The studies indicates that $\tau_q^{(1)}\approx \tau_q^{(2)}= \tau_q^{(1,2)}$ while it appears that $\tau_q^{(3)}< \tau_q^{(1,2)}$ which can be related to a reduced electron density in the third subband.\\ This work was supported by the National Science Foundation (DMR 1104503), the Russian Foundation for Basic Research (project no.14-02-01158) and the Ministry of Education and Science of the Russian Federation. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 12:39PM |
G5.00007: Investigation of Quantum Anomalous Hall Effect in Magnetic Topological Insulators Xufeng Kou, Yabin Fan, Lei Pan, Kang Wang, Shih-Ting Guo, Wei-Li Lee, Ting-Kuo Lee, Eun-Sang Choi, Ying Jiang, Yong Wang We investigate the quantum anomalous Hall Effect (QAHE) and related chiral transport in the MBE-grown Cr-doped (BiSb)$_{2}$Te$_{3}$ thin films. With high sample quality and robust magnetism at low temperatures, the quantized Hall conductance of $e^{2}/h$ is realized up to 300 mK. Meanwhile, the Chern insulator-featured chiral edge conduction is manifested by the non-local transport measurements. We find that the QAHE edge transport depends on both the current direction and magnetization, and its chiral feature can be well-described by the Landauer-B\"{u}ttiker equation. Unlike the helical edge channels in the quantum spin Hall (QSHE) state, the QAHE state is robust against the momentum and energy relaxation, and the dissipationless chiral edge conduction persists on the macroscopic scale. Our results are consistent with the QAHE theory, and the chiral edge channel transport may pave a new way towards ideal low-power interconnect applications. [Preview Abstract] |
Tuesday, March 3, 2015 12:39PM - 12:51PM |
G5.00008: Enhancement of spin susceptibility of low-density two-dimensional electrons in a high quality Si/SiGe quantum well Tzu-Ming Lu, Xiaoyan Shi, Wei Pan, Shi-Hsien Huang, CheeWee Liu, Jiun-Yun Li We report magneto-transport measurement results of two-dimensional electrons in a high quality Si/SiGe quantum well under tilted magnetic fields. The electron peak mobility reaches 2 x 10$^{6}$ cm$^{2}$/Vs and the density is varied from 0.8 to 2.1 x 10$^{11}$ cm$^{-2}$. Under tilted magnetic fields, two Landau levels with opposite spins are brought into energetic coincidence. From the coincidence angles we determine the effective spin susceptibility g*m*. At n $=$2.1 x 10$^{11}$ cm$^{-2}$, g*m* $\sim$ 4 (in units of m$_{\mathrm{b}}$g$_{\mathrm{b}})$, consistent with previous work [Lai et al, PRL 96, 076805 (2006)]. Our results further show that the spin susceptibility is enhanced by 20{\%} at 0.8 x 10$^{11}$ cm$^{-2}$ from its high density value. Surprisingly, unlike previous results in modulation doped Si/SiGe quantum wells, a resistance peak is observed at nu$=$3 when Landau level coincidence occurs in our undoped Si/SiGe field-effect transistor sample. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, March 3, 2015 12:51PM - 1:03PM |
G5.00009: Experimental Study of Low Density Quantum Hall Fabry-Perot Interferometer Simas Glinskis, Sanghun An, Woowon Kang, Leonidas Ocola, Loren Pfeiffer, Ken West, Kirk Baldwin In this talk we report on study of interference oscillations observed in Fabry-Perot $1.5 \mu m$ diameter interferometers fabricated from low density, high mobility AlGaAs/GaAs heterostructures. The Fabry-Perot interferometers were fabricated using e-beam lithography and inductively coupled plasma etching to minimize sample damage. Optimization of the quantum point contacts were made by systematically varying the etching depth and monitoring the resistance of the device. So far we have been able to detect clear interference oscillations which are observed at integer quantum Hall states. The interference oscillations occur in the low magnetic field side of the Hall plateaus when there is substantial backscattering at the quantum point contacts. A linear relationship between filled Landau levels and oscillation frequencies establishes that our interferometers are in the Coulomb dominated regime described by the interacting model of quantum Hall Fabry-Perot interferometers. Study of interference oscillations in the fractional quantum Hall states are currently under progress and will be discussed. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:15PM |
G5.00010: Theory of Transport Phenomena in Coherent Quantum Hall Bilayers Allan H. MacDonald, Hua Chen, Inti Sodemann We will describe a theory that allows to understand the anomalous transport properties of the excitonic condensate state occurring in quantum quantum Hall bilayers in terms of a picture in which the condensate phase is nearly uniform across the sample, and the strength of condensate coupling to interlayer tunneling processes is substantially reduced compared to the predictions of disorder-free microscopic mean-field theory. These ingredients provide a natural explanation for recently established I-V characteristics which feature a critical current above which the tunneling resistance abruptly increases and a non-local interaction between interlayer tunneling at the inner and outer edges of Corbino rings. We propose a microscopic picture in which disorder is the main agent responsible for the reduction of the effective interlayer tunneling strength. [Preview Abstract] |
Tuesday, March 3, 2015 1:15PM - 1:27PM |
G5.00011: Transient Features in Charge Fractionalization and Non-equilibrium Bosonization Bernd Rosenow, Alexander Schneider, MIrco Milletari In quantum Hall edge states and in other one-dimensional interacting systems, charge fractionalization can occur due to the fact that an injected charge pulse decomposes into eigenmodes propagating at different velocities. If the original charge pulse has some spatial width due to injection with a given source-drain voltage, a finite time is needed until the separation between the fractionalized pulses is larger than their width. In the formalism of non-equilibrium bosonization, the above physics is reflected in the separation of initially overlapping square pulses in the effective scattering phase. When expressing the single particle Green function as a functional determinant of counting operators containing the scattering phase, the time evolution of charge fractionalization is mathematically described by functional determinants with overlapping pulses. We develop a framework for the evaluation of such determinants, and compare our theoretical results with recent experimental findings. [Preview Abstract] |
Tuesday, March 3, 2015 1:27PM - 1:39PM |
G5.00012: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 1:39PM - 1:51PM |
G5.00013: Negative differential conductivity induced current instability in two-dimensional electron gas system in high magnetic fields Ching-Ping Lee, Susumu Komiyama, Jeng-Chung Chen High mobility two-dimensional electron gas (2DEG) formed in the interface of a GaAs/AlGaAs hetero-structure in high magnetic field ($B$) exhibits interring nonlinear response either under microwave radiation or to a dc electric field ($E$). It is general believed that this kind nonlinear behavior is closely related to the occurrence of negative-differential conductance (NDC) in the presence of strong $B$ and $E$. We observe a new type NDC state driven by a direct current above a threshold value ({\boldmath $I_{th}$}) applied to a 2DEG as a function of $B$ at relatively high temperatures ($T$). A current instability is observed in 2DEG system at high \textit{B}$\sim$6-8 T and at high $T$ $\sim$ 20- 30 K while the applied current is over {\boldmath $I_{th}$}. The longitudinal voltage $V_{xx}$ shows sub-linear behavior with the increase of \textbf{\textit{I}}. As the current exceed {\boldmath $I_{th}$}, $V_{xx}$ suddenly drops a $\Delta V_{xx}$ and becomes irregular associated with the appearance of hysteresis with sweeping \textbf{\textit{I}}. We find that {\boldmath $I_{th}$} increases with the increase of $B$ and of $T$; meanwhile, $\Delta V_{xx}$ is larger at higher $B$ but lower $T$. Data analysis suggest that the onset of voltage fluctuation can be described by a NDC model proposed by Kurosawa \textit{et al. } in 1976. The general behaviors of $T$ and $B$ dependence of current instability are analog to those recently reported at lower both $T$ and $B$. This consistence suggests the same genuine mechanism of NDC phenomena observed in 2DEG system. [Preview Abstract] |
Tuesday, March 3, 2015 1:51PM - 2:03PM |
G5.00014: Hall Viscosity and Momentum Transport in Lattice and Continuum Models of the Integer Quantum Hall Effect in Strong Magnetic Fields Thomas Tuegel, Taylor Hughes Hall viscosity describes non-dissipative transport in systems with broken time-reversal and parity symmetries. We develop a new method for computing the Hall viscosity of lattice systems in strong magnetic fields based on momentum transport, which we compare to the method of momentum polarization used by Tu et al. [Phys. Rev. B 88, 195412 (2013)] and Zaletel et al. [Phys. Rev. Lett. 110, 236801 (2013)] for noninteracting systems. We compare the Hall viscosity of square-lattice tight-binding models in magnetic field to the integer quantum Hall effect (IQHE) showing agreement when the magnetic length is much larger than the lattice constant, but deviation as the magnetic field strength increases. We also relate the Hall viscosity of relativistic electrons in magnetic field (the Dirac IQHE) to the conventional IQHE. The Hall viscosity of a lattice Chern insulator in magnetic field agrees with the Dirac Hall viscosity when the magnetic length is much larger than the lattice constant. We also show that the Hall viscosity of the lattice model deviates further from the continuum model if the $C_4$ symmetry of the square lattice is broken to $C_2$, but the deviation is again minimized as the magnetic length increases. [Preview Abstract] |
Tuesday, March 3, 2015 2:03PM - 2:15PM |
G5.00015: Relaxation of the electron wave packet in the quantum Hall edge Artur Slobodeniuk, Edvin Idrisov, Eugene Sukhorukov Recently, single-electron wave packets in the quantum Hall edge (QHE) become very important objects in the so-called electron optics.The properties of these excitations are well known only in the case of free-fermion description of the QHE. The role of the Coulomb interaction in such systems have not received a clear theoretical description yet. We propose the method of calculation of characteristics of single-electron excitations of the QHE which takes into account this interaction. We realise it on the QHE with filling factor $\nu=2$. The difference of the obtained quantum state with the free-fermion answer is investigated. It is shown that role of the Coulomb interaction is crucial and it's effects can be measured in the Hong-Ou-Mandel and Hanburry-Brown-Twiss experiments. As an example, the influence of Coulomb interaction for the case of electronic Mach-Zehnder interferometer is calculated. [Preview Abstract] |
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