Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J11: Fractional Quantum Hall Effect I |
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Sponsoring Units: FIAP Chair: Nikolai Zhitenev, National Institute of Standards and Technology Room: D222 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J11.00001: The Real-Space Entanglement Spectra of Fractional Quantum Hall States A. Chandran, Parsa Bonderson, Nicolas Regnault, Andrei Bernevig We investigate the entanglement spectra arising from a sharp real-space cut on the topologically ordered fractional quantum hall (FQH) ground states. We find that the counting of the real-space entanglement spectra (the number of edge excitations of the liquid) is identical to the number of bulk quasihole excitations, in accordance with the bulk-boundary correspondence. The spectra of cuts with two edges display the shape and counting of counter-propagating non-interacting modes as well. Initial estimates of the topological entanglement entropy seem to be in agreement with theory. The real-space entanglement spectra also allows us to distinguish between particle-hole conjugate states, providing us with a new probe to interacting edge modes. [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J11.00002: Identification of 331 quantum Hall states with Mach-Zehnder interferometry Chenjie Wang, D.E. Feldman It has been shown recently that non-Abelian states and the spin-polarized and unpolarized versions of the Abelian 331 state may have identical signatures in Fabry-P\'{e}rot interferometry in the quantum Hall effect at filling factor 5/2. We calculate the Fano factor for the shot noise in a Mach-Zehnder interferometer in the 331 states and demonstrate that it differs from the Fano factor in the proposed non-Abelian states. The Fano factor depends periodically on the magnetic flux through the interferometer. Its maximal value is $2\times 1.4e$ for the 331 states with a symmetry between two flavors of quasiparticles. In the absence of such symmetry the Fano factor can reach $2\times 2.3e$. On the other hand, for the Pfaffian and anti-Pfaffian states the maximal Fano factor is $2\times 3.2e$. The period of the flux dependence of the Fano factor is one flux quantum. If only quasiparticles of one flavor can tunnel through the interferometer then the period drops to one half of the flux quantum. We also discuss transport signatures of a general Halperin state with the filling factor $2+k/(k+2)$.\\[4pt] [1] Chenjie Wang and D. E. Feldman, Phys. Rev. B {\bf 82}, 165314 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J11.00003: Bulk excitonic currents in a bilayer quantum Hall system and Andreev reflection A.D.K. Finck, J.P. Eisenstein, L.N. Pfeiffer, K.W. West Bilayer 2D electron systems in the quantum Hall regime can support a novel interlayer coherent phase which may be viewed as a Bose condensate of interlayer excitons. While numerous experiments over the past decade have revealed a host of remarkable properties of this strongly correlated quantum fluid, heretofore none have directly demonstrated the transport of excitons across the electrically insulating bulk of the system. We report here just such an observation. Our experimental results show that excitons may be launched into the bulk of the 2D system via a process analogous to Andreev reflection. Excitons are emitted into the bulk of the bilayer when electrons are injected into one 2D layer and withdrawn from the other along a common edge of the system. Similarly, we demonstrate that excitons arriving at the edge of the Hall droplet can drive current through external circuitry connected to contacts along that edge. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J11.00004: Phase diagram of the even-denominator fractional quantum Hall state at $\nu$ = 1/2 in wide quantum wells Javad Shabani, Mansour Shayegan We have studied the fractional quantum Hall (FQH) effect in very high quality two dimensional electrons confined to GaAs single wide quantum wells. In these systems typically two electric subbands are occupied at zero magnetic field and the electron charge distribution in the quantum well is bilayer-like. For a symmetric charge distribution and appropriate electron density, a unique even-denominator FQH state emerges at filling factor $\nu$ = 1/2 which has no counter-part in standard, single-layer systems [1]. We have revisited this problem by studying wide quantum well samples with narrower well widths, $47 \leq w \leq 64$ nm, and hence larger tunneling, $\Delta$ (up to 35 K). The new $\nu$ = 1/2 data in these narrower samples allow us to expand the $d/l_{B}$ vs. $\Delta/(e^{2}/4 \pi \epsilon l_{B})$ phase diagram for the stability of the $\nu$ = 1/2 FQH state (d is the layer distance and $l_{B}$ is the magnetic length). Based on this phase diagram, we find that, it is not clear whether this state has a Pfaffian or a two-component Halperin origin. \\[4pt] [1] Y. W. Suen et al., Phys. Rev. Lett. 72, 3405 (1994). [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J11.00005: When is the fractional quantum Hall effect stable Yang Liu, Javad Shabani, Mansour Shayegan The fractional quantum Hall (FQH) effect, signaled by the vanishing of the longitudinal resistance and the quantization of the Hall resistance, is the hallmark of interacting two-dimensional electrons in a large perpendicular magnetic field. The effect is most prominently observed at low Landau level (LL) filling factors ($\nu$) and is conspicuously absent for $\nu>4$. We examine the stability of the FQH states at high fillings in a 2D electron system in a wide GaAs quantum well which we can tune the Fermi energy ($E_F$) to lie, at a given filling factor, in different LLs of two electric subbands. The data provide direct and definitive evidence that the stability of the FQH states is linked to the LL where $E_F$ resides. We observe FQH states at high filling factors such as 13/3, 14/3, 16/3, and 17/3, but only when $E_F$ lies in the ground state ($N=0$) orbital LLs of either of the two electric subbands, regardless of the underlying, fully occupied levels. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J11.00006: Evolution of odd-denominator fractional quantum Hall states in a two-subband system Mansour Shayegan, Javad Shabani, Yang Liu Our magneto-transport measurements reveal that the sequence of fractional quantum Hall (FQH) states observed in two-subband, wide GaAs quantum wells at high fillings ($\nu >$ 2) are very different from those of a single-subband system. When the Fermi level lies in the lowest Landau level of either of the two subbands the odd-denominator FQH states following the usual, composite fermion filling sequences are observed. These include states at $\nu $ = 7/3, 8/3, 12/5, 13/5, 10/3, 11/3, 17/5, 18/5, and 25/7. The evolution of these states with changing the Zeeman and subband energies is consistent with coincidences of composite fermion Landau levels. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J11.00007: Negative spin wave dispersion for composite fermions U. Wurstbauer, D. Majumder, S. Mandal, I. Dujovne, A. Rigosi, T.D. Rhone, B. Dennis, K. West, L. Pfeiffer, J. Jain, A. Pinczuk The FQHE is a result of strongly interacting electrons that can be understood as QHE of composite fermions. We use inelastic light scattering experiments to study the collective excitations of CF with 2 flux quanta focusing on filling factors $\nu$ = 4/9, 3/7 and 2/5. For these fillings, the lowest collective excitation modes are spin-waves, which display a distinct spectral weight below the bare Zeeman energy indicating a negative dispersion relation. The determined energies for these ``spin-wave roton minima'' are in excellent quantitative agreement with numerical calculations. Using the real experimentally transferred momentum the addressed DOS and hence inelastic light scattering spectra can be modeled. We demonstrate that the observed modes are very similar for positive and negative effective magnetic field at the same CF-filling factor. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J11.00008: Subband Engineering Even-Denominator Quantum Hall States Vito Scarola, Christian May, Michael Peterson, Matthias Troyer Proposed even-denominator fractional quantum Hall effect (FQHE) states suggest the possibility of excitations with non-Abelian braid statistics. Recent experiments on wide square quantum wells observe even-denominator FQHE even under electrostatic tilt. We theoretically analyze these structures and develop a procedure to accurately test proposed quantum Hall wavefunctions. We find that tilted wells favor partial subband polarization to yield Abelian even-denominator states. Our results show that tilting quantum wells effectively engineers different interaction potentials allowing exploration of a wide variety of even-denominator states. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J11.00009: Quasiparticle tunneling amplitute in fractional quantum Hall states Zixiang Hu, Kihoon Lee, Edward H. Rezayi, Xin Wan, Kun Yang We study qp tunneling in the MR state, in which qp of charge e/4 and e/2 may co-exist and both contribute to edge transport. The tunneling amplitude for charge e/2 qp is exponentially smaller than that for e/4 qh, and the ratio between them can be (partially) attributed to their charge difference. The tunneling amplitude shows some scaling behavior which originates from the propagation and tunneling of charged qhs in an effective field analysis. In the ring limit, we conjecture the exact functional form for several cases. The results for Abelian qp tunneling is consistent with the scaling anaysis; this allows for the extraction of conformal dimensions of the qps. We analyze the scaling behavior of both Abelian and non-Abelian qps in the Z$_k$ parafermion states. Interestingly, the non-Abelian qp tunneling amplitudes exhibit nontrivial $k$-dependent corrections to the scaling exponent. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J11.00010: Extracting Excitations From Model State Entanglement Nicolas Regnault, Antoine Sterdyniak, Andrei Bernevig We extend the concept of entanglement spectrum from the geometrical to the particle bipartite partition. We apply this to several Fractional Quantum Hall wavefunctions on both sphere and torus geometries to show that this new type of entanglement spectra completely reveals the physics of bulk quasihole excita tions. While this is easily understood when a local Hamiltonian for the model state exists, we show that the quasiholes wavefunctions are encoded within the model state even when such a Hamiltonian is not known. As a nontrivial example, we look at Jain's composite fermion states and obtain their quasiholes directly from the model state wavefunction. We reach similar conclusions for wavefunctions described by Jack polynomials. [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J11.00011: Neutral mode heat transport and fractional quantum Hall shot noise So Takei, Bernd Rosenow We study nonequilibrium edge state transport in the fractional quantum Hall (FQH) regime for states with a counter-propagation neutral mode. Focusing on the filling fraction of 2/3, we consider a setup in which the neutral mode is heated by a hot spot, and where heat transported by the neutral mode causes a temperature difference between the upper and lower edges in a Hall bar. This temperature difference is probed by the excess noise it causes for scattering across a quantum point contact (QPC). We find that the excess noise in the QPC provides evidence for counter-propagating neutral modes, and we calculate its dependence on both the temperature difference between the edges and on source drain bias. We generalize our results to the non-abelian Moore-Read quantum Hall state at filling fraction 5/2. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J11.00012: Anisotropic quantum Hall liquids - a small system Monte Carlo study Orion Ciftja, Brittney Cornelius, Kesha Brown, Emery Taylor While no fractional quantum Hall effect states were expected to stabilize in the second excited Landau level, the discovery of extreme magneto-transport anisotropy around filling factor 9/2 was found quite surprising. A unidirectional charge density wave is a plausible candidate for the anisotropic states as indicated by the earlier theoretical work. An alternative approach that would be consistent with observed experimental facts would view the onset of anisotropy as signature of a phase transition from an isotropic to an anisotropic liquid crystalline phase. In this work we present a small-system Monte Carlo study for anisotropic quantum Hall liquid states observed at filling factor 9/2. The anisotropic electronic liquid phases are described by a broken rotational symmetry wave function and electrons interact with Landau level-projected interaction potentials. Our small-system Monte Carlo study indicates that such an anisotropic liquid crystalline quantum Hall phase with broken rotational symmetry is energetically favored relative to an isotropic liquid one. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J11.00013: Chiral Abelian anyons from interacting non-Abelian vortices Ville Lahtinen, Jiannis Pachos We demonstrate the existence of a new topologically ordered phase in Kitaev's honeycomb lattice model. This new phase appears due to the presence of a tightly packed vortex lattice and it supports chiral Abelian anyons. We characterize the phase by its low-energy behavior that is described by four Fermi points as opposed to two Fermi points in the absence of the vortex lattice. This doubling is shown to be related to an emergent vortex lattice symmetry that arises due to interactions between the anyonic vortices. By mapping the Hamiltonian of the model to a BCS one, we show that the chiral Abelian phase can be understood as two coupled p-wave superconductors, one living on the original honeycomb lattice and the other on the dual lattice that coincides with the vortex lattice. Finally, we identify two physically distinct types of topological phase transitions in the model and show that the Fermi surface evolution associated with them is described by Dirac fermions coupling to chiral gauge fields. The study of the Fermi point transport across the Brillouin zone enables us to obtain analytic results on the extended phase space. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J11.00014: The Weakly Coupled Pfaffian as a Type I Quantum Hall Liquid S.A. Parameswaran, S.A. Kivelson, S.L. Sondhi, B.Z. Spivak The Pfaffian phase of electrons in the proximity of a half-filled Landau level is understood to be a $p+ip$ superconductor of composite fermions. We consider the properties of this paired quantum Hall phase when the pairing scale is small, {\it i.e.} in the weak-coupling, BCS, limit, where the coherence length is much larger than the charge screening length. We find that, as in a Type I superconductor, the vortices attract so that, upon varying the magnetic field from its magic value at $\nu=5/2$, the system exhibits Coulomb frustrated phase separation. We propose that the weakly and strongly coupled Pfaffian states exemplify a general dichotomy between Type I and Type II quantum Hall fluids. [Preview Abstract] |
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