Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L43: New Developments in the FQHE in Half-filled Landau LevelsInvited
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Sponsoring Units: DCMP Room: BCEC 210B |
Wednesday, March 6, 2019 11:15AM - 11:51AM |
L43.00001: Observation of half-integer thermal Hall conductance Invited Speaker: Moty Heiblum Quantum mechanics sets an upper bound on the amount of charge flow as well as on the amount of heat flow in ballistic one-dimensional channels. The two relevant upper bounds, that combine only fundamental constants, are the quantum of the electrical conductance, Ge=η e2/h with η =e*/e and the quantum of the thermal conductance, Gth=k0T=(π2kB2/3h)T [1]. Remarkably, the latter does not depend on particles charge; particles statistics; and even the interaction strength among the particles [2]. |
Wednesday, March 6, 2019 11:51AM - 12:27PM |
L43.00002: Fractional Quantized Hall States with Even Denominator Invited Speaker: Bertrand I. Halperin Even-denominator fractional quantized Hall states have been seen in a variety of systems. In addition to the well-known states at filling fractions ν = 5/2 and 7/2 observed in GaAs narrow wells, even-denominator quantized states have been seen in Bernal-stacked bilayer graphene, in ZnO, and in GaAs double layers and wide quantum wells at total filling νtotal = ½. The precise nature of the quantized Hall states is a matter of debate in all these cases, and I will discuss some of the alternative theories. There is another case, however, where the situation is clear. Recent experiments on a system of two graphene layers separated by a thin insulator find, among other states, a quantized Hall state with filling ν = ¼ in each layer. Measurements of a quantized Hall drag, as well as quantized Hall resistance, show that the system has the characteristics of the 331 Abelian state.1 [1] Xiaomeng Liu, Zeyu Hao, K. Watanabe, T. Taniguchi, B. Halperin, and P. Kim, arXiv:1810.08681. |
Wednesday, March 6, 2019 12:27PM - 1:03PM |
L43.00003: Theory of disorder-induced half-integer thermal Hall conductance Invited Speaker: David Mross Thermal Hall conductance in the half-filled first Landau level was recently measured to take the quantized non-integer value kappa=5/2, which indicates a non-Abelian phase of matter. Such exotic states have long been predicted to arise at this filling factor, but the measured value disagrees with numerical studies, which predict kappa=3/2 or 7/2. I will briefly review the contradictory experimental and theoretical findings and discuss how they may be reconciled. Specifically, I will describe a possible resolution based on disorder-induced formation of mesoscopic puddles. Interactions between these puddles can generate a coherent macroscopic state that exhibits a plateau with quantized kappa=5/2 and non-Abelian quasiparticles that are distinct from those of the microscopic puddles. |
Wednesday, March 6, 2019 1:03PM - 1:39PM |
L43.00004: Even denominator fractional quantum Hall physics in higher order Landau levels of graphene Invited Speaker: Jurgen Smet An important development in the field of the fractional quantum Hall effect has been the proposal that the 5/2 state observed in the Landau level with orbital index n = 1 of two-dimensional electrons in a GaAs quantum well originates from a chiral p-wave paired state of composite fermions which are topological bound states of electrons and quantized vortices. This state is theoretically described by a ``Pfaffian" wave function or its hole partner called the anti-Pfaffian, whose excitations are neither fermions nor bosons but Majorana quasiparticles obeying non-Abelian braid statistics. This has inspired innovative ideas for computation and has also instigated a quest for other states with exotic quasiparticles. Here we report experiments on monolayer graphene that show clear evidence for unexpected even-denominator fractional quantum Hall physics in the n = 3 Landau level. We numerically investigated the known candidate states for even-denominator fractional quantum Hall effect, including the Pfaffian, the particle-hole symmetric Pfaffian, the 221-parton, and several valley/spin singlet states. We conclude that, among these, the 221-parton state is a possible candidate to explain the experimentally observed state and that this incompressible ground state is distinct from the 5/2 state in GaAs . Like the Pfaffian, this state is also believed to harbour quasi-particles with non-Abelian braid statistics. |
Wednesday, March 6, 2019 1:39PM - 2:15PM |
L43.00005: The Dirac Composite Fermion of the Fractional Quantum Hall Effect Invited Speaker: Dam Thanh Son TBD |
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