Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V37: QHE and FQHE |
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Sponsoring Units: FIAP Chair: Wei Pan, Sandia National Laboratories Room: Morial Convention Center 229 |
Thursday, March 13, 2008 11:15AM - 11:27AM |
V37.00001: Optical Studies of Quantum Phases with Filling Factors 2$\le \nu \le $3 in the Second Landau Level Trevor David Rhone, Jun Yan, Yann Gallais, Aron Pinczuk, Loren Pfeiffer, Ken West We report low temperature inelastic light scattering and optical recombination measurements of quantum phases in the second Landau level of 2D electron systems. We focus on states with filling factors 2$\le \nu \le $3. An ultra high mobility, high density GaAs quantum well (240nm) is probed at low temperature (42mK -- 1.2K). Low energy spin excitations are studied by resonant inelastic light scattering. We confirm the existence of a ferromagnetic state at $\nu $ = 3 by the observation of a well-defined long wavelength spin wave mode at the Zeeman energy. Surprisingly, the ferromagnetic spin wave collapses at filling factors slightly away from $\nu $ = 3. While this behavior may be a signal of the disappearance of ferromagnetic order in the second Landau level, experiments in progress may offer deeper insights on fundamental interactions and quantum phases in the second Landau level. [Preview Abstract] |
Thursday, March 13, 2008 11:27AM - 11:39AM |
V37.00002: Investigations of possible Landau level anticrossings in p-type (110) GaAs square wells Nebile Isik, S.F. Roth, M. Bichler, A. Fontcuberta i Morral, G. Abstreiter, M. Grayson In p-type (110) quantum wells, a single anomalous magnetoresistance peak is observed within the lowest Landau level ($\nu= 1$) of a two-dimensional hole system when the confinement is a triangular potential well [1]. This peak is interpreted as the transport signature of a $\pm$ 3/2 spin-reversal level-anticrossing in the lowest Landau level. In recently fabricated 400 \AA wide square quantum wells, we observe peaks within several Landau levels, for example, at both $\nu=1$ and $\nu=2$. The peak positions in magnetic field $B$ are observed shift with top gate bias and the peak magnitudes are observed to increase with increasing temperature. At a critical top gate bias, however, both original peaks disappear, just as new features appear at higher fields within both the $\nu=1$ and $\nu=2$ minima. Dependence of feature position on front and back gate bias will be shown, and temperature dependences will be studied in terms of activated energy gaps. The cause of these peaks will be discussed in terms of possible multiple Landau level anticrossings. \newline [1] F. Fischer, R. Winkler, D. Schuh, M. Bichler, G. Abstreiter and M. Grayson Phys. Rev. B 75, 073303 (2007). [Preview Abstract] |
Thursday, March 13, 2008 11:39AM - 11:51AM |
V37.00003: Current Instability Induced by Negative Differential Conductivity in the Quantum Hall Regime Kuan Ting Lin, Yuling Tsai, Yiping Lin, J. C. Chen, T. Ueda, S. Komiyama We report a new kind of nonlinear effect at $\nu=2$ Hall plateau in a two-dimensional electron gas system formed on a GaAs/Al$_{0.3}$Ga$_{0.7}$As heterostructure. Within the temperature 16 K $\leq$ T $\leq$ 28 K, the current shows discernible zig-zag feature as the applied dc electric field increases beyond a critical value. Such an unstable feature is not only reproducible but also exhibits hysteresis as changing the sweeping direction of the electric field. We identify this current instability as the occurrence of the negative differential conductivity induced by the electric field. Physical origin of the nonlinearities will be presented and discussed. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V37.00004: New Observations in the $N\ge1$ Landau Levels of Wide GaAs Quantum Wells D.R. Luhman, W. Pan, D.C. Tsui, L.N. Pfeiffer, K.W. Baldwin, K.W. West We have studied a series of high-quality wide GaAs/AlGaAs quantum wells at various tilt angles ($\theta$) with respect to magnetic field. Several interesting observations have been made when the Landau level index is $N\ge1$. The quantum Hall states corresponding to total odd filling factors are seen to be reentrant with increasing $\theta$, i.e. they disappear and reemerge as $\theta$ is increased. This observation can be explained by considering oscillations in the tunnelling amplitude with increasing $\theta$. As $\theta$ is increased further, anisotropy emerges at values of half filling. This is particularly visible in the $N=1$ Landau level at total filling factors $\nu=9/2$ and $11/2$. For even larger values of $\theta$, anisotropy develops at $\nu=5$ followed by $\nu=7$. We will discuss how each of these observations are effected by quantum well width and also in the context of previous theoretical and experimental results. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V37.00005: Edge state tunneling in a point contact at filling fraction $\nu$=5/2 Iuliana P. Radu, J.B. Miller, C.R. Dillard, C.M. Marcus, M.A. Kastner, L.N. Pfeiffer, K.W. West We investigate low temperature transport properties of quantum point contacts (QPCs) fabricated in a GaAs/AlGaAs 2-dimensional electron gas (2-DEG) with mobility 2000 m$^{2}$/Vs in a perpendicular magnetic field. The 2-DEG exhibits fractional quantum Hall effect, including a well-quantized plateau at $\nu$=5/2. We study the temperature and DC current bias dependence of the transport through the QPC at $\nu$=5/2 while preserving the same filling number in both the QPC and the bulk of the sample. We compare our results to theoretical predictions for quasi-particle tunneling in the weak coupling regime, and extract the quasi-particle charge and the strength of the Coulomb interaction, as reflected by the Luttinger liquid parameter $g$. This work was partially supported by ARO (W911NF-05-1-0062), by the NSEC program of NSF (PHY-0117795), by NSF (DMR-0353209) at MIT and by Project Q of Microsoft Corporation at Harvard University. [Preview Abstract] |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V37.00006: Stripes and Bubbles in the N=2 Landau Level: A DMRG Study Barry Friedman, Lauren Rod, Candice Withrow The phase diagram of the N=2 Landau level has been reexamined using the density matrix renormalization group (dmrg). Very good agreement at filling factor 18/42 has been attained with previous dmrg calculations of Shibata and Yoshioka by using 200 states in the blocks. Near 1/2 filling, we have studied whether the ground state is an anisotropic crystal, suggested by some mean field approaches, or a stripe state, as suggested by other mean field approaches and previous dmrg results. Previous dmrg calculations, i.e. Shibata and Yoshioka, have placed the phase diagram between stripes and bubbles at a filling factor slightly less then .4 by looking at the projected pair correlation function at the special lines x=0 and y=0. We reexamine this boundary by studying the Fourier transform of the projected pair correlation. [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 12:39PM |
V37.00007: Interactions and Landau level mixing at large half odd-integer filling Peter Smith, Malcolm Kennett Recent transport experiments on two-dimensional hole systems (2DHSs) in a strong perpendicular magnetic field show variations in the anisotropy of resistivity at half odd-integer filling fractions $\nu$=7/2, 9/2, and 11/2 that differ from those seen in two-dimensional electron systems \footnote[1]{M. J. Manfra et al., Phys. Rev. Lett. {\bf 98}, 206804 (2007).}. It has been suggested that spin-orbit coupling in 2DHSs leads to these unusual transport properties, as it gives rise to Landau level mixing. We consider the general problem of interacting fermions subject to a perpendicular magnetic field with Landau level mixing in the limit of large Landau levels, and discuss the effect of Landau level mixing on charge-density wave formation in comparison to the single Landau level case \footnote[2]{R. Moessner and J. T. Chalker, Phys. Rev. B. {\bf 54}, 5006 (1996).}. We study the case of spin-orbit induced mixing in detail, and discuss implications for experiments. [Preview Abstract] |
Thursday, March 13, 2008 12:39PM - 12:51PM |
V37.00008: Interaction effects in transport through an electronic Mach-Zehnder interferometer Vitaly Golovach, Florian Marquardt We study theoretically transport through an electronic Mach-Zehnder interferometer in the presence of Coulomb interaction inside the interferometer, using a discrete wave-packet model. We find that the mutual capacitance between the arms of the interferometer leads to a suppression of the visibility of the Aharonov-Bohm oscillations at a large source-drain bias $\Delta\mu\gg\hbar v_F/L$, where $L$ is the length of the arms and $v_F$ is the electron drift speed. Our numerical simulations indicate that the visibility of the Aharonov-Bohm oscillations is a non-analytic function of the mutual capacitance strength, in the limit $\Delta\mu\to\infty$. [Preview Abstract] |
Thursday, March 13, 2008 12:51PM - 1:03PM |
V37.00009: Universal Periods in Quantum Hall Droplets Gregory A. Fiete, Gil Refael, Matthew P. A. Fisher Using the hierarchy picture of the fractional quantum Hall effect, we study the the ground state periodicity of a finite size quantum Hall droplet in a quantum Hall fluid of a different filling factor. The droplet edge charge is periodically modulated with flux through the droplet and will lead to a periodic variation in the conductance of a nearby point contact, such as occurs in some quantum Hall interferometers. Our model is consistent with experiment and predicts that superperiods can be observed in geometries where no interfering trajectories occur. The model may also provide an experimentally feasible method of detecting elusive neutral modes and otherwise obtaining information about the microscopic edge structure in fractional quantum Hall states. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V37.00010: Variational Monte Carlo study of the nematic state at half-filled Landau level of the two dimensional electron gas Quoc Doan, Efstratios Manousakis The nematic state of 2DEG at half-filled Landau level (LL) is
investigated using the variational Monte Carlo method. The
wavefunction used has Jastrow correlations of the form
$\prod_{i |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V37.00011: Anisotropy in two-dimensional electronic quantum Hall systems at half filling of valence Landau levels Orion Ciftja, Carlos Wexler A recent experimental discovery in the quantum Hall regime has been the observation of very strong magneto-transport anisotropies at certain low values of magnetic field below a critical temperature of about 100 mK. While the origin of such anisotropy is yet unknown, we explain the emergence of such anisotropies in terms of electronic liquid crystalline states with broken rotational symmetry. We investigate the stability of liquid crystalline phases with nematic order at half filling of the valence Landau level. Quantum Monte Carlo simulations indicate that while isotropic states are stable in the lowest and first excited Landau level, there are regions of instability towards liquid crystalline states in higher Landau levels. A possible connection of the recently discovered magneto-transport anisotropy in low magnetic fields and these liquid crystalline states is discussed. [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V37.00012: Quantum Hall hierarchy wave functions from conformal field theory Susanne Viefers, Emil Bergholtz, Hans Hansson, Maria Hermanns, Anders Karlhede It has long been known that Laughlin's wave functions, describing the fractional quantum Hall effect at filling fractions $\nu=1/(2k+1)$, can be obtained as correlation functions in conformal field theory. We show how to generalize this approach to construct explicit trial wave functions for all states in the quantum Hall hierarchy corresponding to quasiparticle (as opposed to quasihole) condensates, including the recently observed state at $\nu = 4/11$. At the filling fractions $\nu = n/(2np+1)$ this construction exactly reproduces Jain's composite fermion wave functions. An explicit connection is made to Wen's topological classification of FQH states. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V37.00013: FQHE-the solvable limit and beyond Maria Hermanns, Emil J. Bergholtz, Thors Hans Hansson, Anders Karlhede, Juha Suorsa We consider the quantum Hall system in the torus geometry. In the limit where the torus becomes thin, the problem is exactly solvable and the hierarchy of quantum Hall states is manifest. Explicit wave functions for a large set of them are constructed with help of conformal field theory. This construction provides a continuation from the exactly solvable limit to the experimental regime. Numerical results on 4/11 supports this picture. [Preview Abstract] |
Thursday, March 13, 2008 1:51PM - 2:03PM |
V37.00014: The Quantum Hall Effect in Spin Quartets in Graphene Keshav Shrivastava Using the non-relativistic Schroedinger equation, we find that for (1/2)g=(1/2)$\pm $s gives zero charge for negative sign and one charge for positive sign. This explains the conductivity at i = 0 and 1. For s=3/2, (1/2)g=2 for positive sign and hence g=4. The substitution in the series, -(5/2)(g$\mu _{B}$H), -(3/2)(g$\mu _{B}$H), -(1/2)( g$\mu _{B}$H), +(1/2)( g$\mu _{B}$H),+(3/2)( g$\mu _{B}$H), +(5/2)( g$\mu _{B}$H), {\ldots}, etc., g=4 gives, -10, -6, -2, +2, +6, +10, etc. This series is the same as observed in the experimental data of quantum Hall effect in graphene. When we take n=2 in the flux quantization, i.e., 2(hc/e), we generate the plateaus at $\pm $4. Thus the plateaus can occur at 0, 1, 4 and at 2, 6, 10, 14, {\ldots}, etc. Thus the quantum Hall effect in graphene is understood by means of non-relativistic theory. The fractions such as 1/3 or integers such as 0,1,4,{\ldots}, 2,6,10,14, {\ldots} multiply the charge and hence describe the ``effective charge'' of the quasiparticles. This means that there is ``spin-charge locking''. \begin{enumerate} \item K. N. Shrivastava, Phys. Lett. A 113, 435(1986); 115, 436(E)(1986); Phys. Lett. A, 326, 469(2004); AIP Conf. Proc. 909, 43(2007);909,50(2007. \item Z.Jiang, et al, Phys. Rev. Lett. 98,197403(2007);Y.Zhang et al, Phys. Rev. Lett. 96, 136806(2006). \end{enumerate} [Preview Abstract] |
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