Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Z1: Quasiparticles and non-Abelian Statistics in the 5/2 State |
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Sponsoring Units: DCMP Chair: Gregory Fiete, California Institute of Technology Room: Spirit of Pittsburgh Ballrom A |
Friday, March 20, 2009 11:15AM - 11:51AM |
Z1.00001: Status of Experiments on the 5/2 Quantized Hall State: A Theorist's View Invited Speaker: Bertrand I. Halperin A number of experiments have been proposed, which, at least in principle, should clarify the nature of the fractional quantized Hall state at filling fraction 5/2. For example, experiments might measure the spin polarization of the ground state and the charge of the elementary quasiparticles, and could test whether the quasiparticles indeed obey non-Abelian statistics, as predicted by the Moore-Read model. These experiments are difficult, however, and their interpretation may be complicated by non-uniformities in the electron density and other problems, which also pose difficulties at simpler filling fractions. We shall discuss the current experimental situation, with these issues in mind. [Preview Abstract] |
Friday, March 20, 2009 11:51AM - 12:27PM |
Z1.00002: Fractionally charged quasiparticles at filling fraction 5/2 Invited Speaker: Moty Heiblum_ |
Friday, March 20, 2009 12:27PM - 1:03PM |
Z1.00003: Quasiparticle Tunneling in the Fractional Quantum Hall effect at filling fraction $\nu$=5/2 Invited Speaker: Iuliana P. Radu In a two-dimensional electron gas (2DEG), in the fractional quantum Hall regime, the quasiparticles are predicted to have fractional charge and statistics, as well as modified Coulomb interactions. The state at filling fraction $\nu$=5/2 is predicted by some theories to have non-abelian statistics, a property that might be exploited for topological quantum computing. However, alternative models with abelian properties have been proposed as well. Weak quasiparticle tunneling between counter-propagating edges is one of the methods that can be used to learn about the properties of the state and potentially distinguish between models describing it. We employ an electrostatically defined quantum point contact (QPC) fabricated on a high mobility GaAs/AlGaAs 2DEG to create a constriction where quasiparticles can tunnel between counter-propagating edges. We study the temperature and dc bias dependence of the tunneling conductance, while preserving the same filling fraction in the constriction and the bulk of the sample. The data show scaling of the bias-dependent tunneling over a range of temperatures, in agreement with the theory of weak quasiparticle tunneling, and we extract values for the effective charge and interaction parameter of the quasiparticles. The ranges of values obtained are consistent with those predicted by certain models describing the 5/2 state, indicating as more probable a non-abelian state. This work was done in collaboration with J. B. Miller, C. M. Marcus, M. A. Kastner, L. N. Pfeiffer and K. W. West. This work was supported in part by the Army Research Office (W911NF-05-1-0062), the Nanoscale Science and Engineering Center program of NSF (PHY-0117795), NSF (DMR-0701386), the Center for Materials Science and Engineering program of NSF (DMR-0213282) at MIT, the Microsoft Corporation Project Q, and the Center for Nanoscale Systems at Harvard University. [Preview Abstract] |
Friday, March 20, 2009 1:03PM - 1:39PM |
Z1.00004: Measurement of filling factor 5/2 quasiparticle interference Invited Speaker: Robert Willett A 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 computation. Interferometric devices may be employed to manipulate and measure quantum Hall edge excitations. Here we use a small area edge state interferometer designed to observe quasiparticle interference effects. Oscillations in transmission consistent in detail with the Aharanov-Bohm effect are observed for integer and fractional quantum Hall states (filling factors 2, 5/3 and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these charge calibrations, at filling factor 5/2 and at lowest temperatures periodic transmission through the device consistent with quasiparticle charge e/4 is observed. The principal finding of this work is that in addition to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at filling factor 5/2 and at lowest temperatures. Properties of the e/4 and e/2 oscillations at 5/2 are examined with the device sensitivity sufficient to observe the relative prevalence of e/4 and e/2 oscillations, transitions between the periods, and temperature evolution of the 5/2 quasiparticle interference. Among possible etiologies, this presence of an effective e/2 period may empirically reflect an e/2 quasiparticle charge, or may reflect multiple passes of the e/4 quasiparticle around the interferometer. These results are discussed within a potential picture of e/4 quasiparticle excitations possessing non-Abelian statistics. Some critical consistencies are met between the experimental results and properties of non-Abelian e/4 quasiparticles. These studies demonstrate the capacity to perform interferometry on 5/2 excitations and reveal properties important for understanding this state and its excitations. [Preview Abstract] |
Friday, March 20, 2009 1:39PM - 2:15PM |
Z1.00005: The Anti-Pfaffian and anti-Read-Rezayi States Invited Speaker: Chetan Nayak |
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