Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B07: Integer Quantum Hall 
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Sponsoring Units: DCMP Chair: Javad Shabani, New York University Room: LACC 153B 
Monday, March 5, 2018 11:15AM  11:27AM 
B07.00001: Quantum Transport in Black Phosphorus Twodimensional Hole Gas in High Magnetic Fields Zuocheng Zhang, Fangyuan Yang, Naizhou Wang, Kenji Watanabe, Takashi Taniguchi, Xianhui Chen, Yuanbo Zhang Black phosphorus has recently emerged as a new twodimensional (2D) material with a direct bandgap and high carrier mobilities. In this talk we present our transport study of black phosphorus 2D hole gas in high magnetic fields. We observe welldefined quantized plateaus in Hall resistance, accompanied by vanishing magnetoresistance; both are hallmarks of the quantum Hall effect. More importantly, we observed, for the first time, new states at fractional filling factors that originate from the strong anisotropy in black phosphorus. We will discuss the link between the new states and the charge density wave states observed in conventional 2D electron systems. 
Monday, March 5, 2018 11:27AM  11:39AM 
B07.00002: Landau Level Energy Gaps in Ultrahigh Quality Black Phosphorus Devices Son Tran, Jiawei Yang, Jason Wu, Hongwoo Baek, Dmitry Smirnov, Takashi Taniguchi, Kenji Watanabe, Ruoyu Chen, Chun Ning Lau We report black phosphorus (BP) field effect transistors with low temperature record field effect mobility up to 55,000 cm^{2}/Vs. Thanks to the ultrahigh device quality, the integer quantum Hall effect is observed with full spin degeneracy lifting over a wide range of magnetic field 10 T – 45 T. Landau level (LL) energy gaps of filling factors ν=1, 2, 3, 4, 5, and 6 are measured and demonstrate a linear dependence on magnetic field. This settles a theoretical controversy on the effects of BP’s anisotropic crystal structure on its LL energetics. 
Monday, March 5, 2018 11:39AM  11:51AM 
B07.00003: Transport Properties Of Near Surface Quantum Wells In InAs Heterostructures Joseph Yuan, William Mayer, KAUSHINI WICKRAMASINGHE, Javad Shabani We study transport properties of 2 dimensional electron gases (2DEG) confined in a quantum well (QW) just below the surface. These quantum wells allow a wide variety of new applications including epitaxial contact to superconducting metals such as Al and Nb. In this work we study Dingle mobility and Landau level broadening of these samples and examine missing odd integer quantum Hall states at high magnetic field. We also analyze the weak antilocalization signal and extract information about spin orbit coupling which provide a foundation for future measurements involving topological superconductivity. 
Monday, March 5, 2018 11:51AM  12:03PM 
B07.00004: Strong equilibration of Landau level edge states at the physical edge of graphene Curt Richter, Son Le, Joseph Hagmann, Nikolai Klimov, Ji Ung Lee, David Newell We report on the interaction of quantized Landau level (LL) edge states in graphene devices at both electrostatically defined edges of a pn junction (pnJ) and the physical edge of graphene. To determine these interactions, magnetotransport measurements were made on a graphene pnJ device with a ring shape geometry in the quantum Hall regime. Nonequilibrium conditions of the LL edgestates are established by decoupling the edgestate of the energetically lowest LL from the higher LLs at one pnJ interface. [1] Due to the chirality of these edge channels determined by the direction of the magnetic field and the charge of the carriers (n or ptype) they then pass along the abrupt physical inner edge of the graphene ring before reaching a second pnJ which probes the level of equilibration between the lowest LL and the others. Our measurements show that, while the lowest LL edge state is decoupled from the other LL’s at the electrostatic junction [1], all of the LL edge states strongly equilibrate along the physical edge of the graphene despite the relatively short distance that they travel along this edge. 
Monday, March 5, 2018 12:03PM  12:15PM 
B07.00005: The quantum Hall phase transition at ν_{tot} =1 in graphene double layers Youngwook Kim, Kenji Watanabe, Takashi Taniguchi, Jurgen Smet We investigated the quantum Hall effect in graphene double layers which consist of two stacked graphene monolayers that are slightly rotated with respect to one another. We observe unexpected signatures of interlayer coherence resulting in oddinteger quantum Hall states (QHSs) at a balanced density between the layers (e.g ν_{tot} =1 = 1/2 + 1/2). We attribute the emergence of these QHSs to spontaneous layer coherence driven by interlayer Coulomb interactions, which are tunable using the magnetic field and the layer carrier densities. At fixed field a phase transition from the layer coherent state to the layer incoherent state is induced upon increasing density. This phase transition weakens and finally vanishes with increasing magnetic field. 
(Author Not Attending)

B07.00006: Quantized transport in topological insulator npn junctions Abhishek Banerjee, Ananthesh Sundaresh, R Ganesan, Diptiman Sen, PS Anil Kumar The halfinteger quantum Hall effect is one of the most iconic features of Dirac fermions. Yet, bandstructure degeneracy in graphene (spin and valley) and topological insulators(topbottom surface symmetry) prevents a direct observation of this effect. To this end, we fabricate dual gated devices of the bulk insulating topological insulator BiSbTe_{1.25}Se_{1.75} where gate electrodes are configured to produce npn junctions across the sample surface and also break the topbottom surface inversion symmetry. In the quantum Hall regime, these junctions reveal plateaus in longitudinal resistance at 3/2 and 4/3 times the resistance quantum, h/e^{2}. We model the electrostatics of the system using four distinct filling factors which give rise to six quantum Hall edge modes. Mode mixing between these channels in the unipolar and bipolar regimes gives rise to the observed resistance fractionalization. Specifically, the fractions observed in experiment arise as a direct consequence of the 1/2 integer quantum Hall effect of the Dirac fermions, thereby providing a method to access zeroLL physics in Dirac systems. 
Monday, March 5, 2018 12:27PM  12:39PM 
B07.00007: Skyrmion in the N=0 Landau level of graphene Yunlong Lian, Mark Goerbig Skyrmions are present in multicomponent quantum Hall systems where the splittings of Landau sublevels are small compared to the Coulomb energy. Using a minimal field theory obtained by the variational approach, we study various types of charge1 skyrmions at the vicinity of both quarter filling and half filling of the N=0 Landau level of graphene. We find novel texture states in the spinpseudospinentanglement channel, as well as the transitions between different phases of skyrmions.[1][2] Our studies provide references for STM/STS imaging of the textured quantum Hall states in graphene, and suggest a refined picture for charge transport in the multicomponent quantum Hall systems. We also studied the charge1 skyrmions at halffilling of the N=0 Landau level in graphene monolayer. 
Monday, March 5, 2018 12:39PM  12:51PM 
B07.00008: Integer quantum Hall transitions on tightbinding lattices Martin Puschmann, Philipp Cain, Michael Schreiber, Thomas Vojta

Monday, March 5, 2018 12:51PM  1:03PM 
B07.00009: Secondorder geometric responses and central charge Judith Hoeller, Nicholas Read We extend the study of Hall viscosity and thermal Hall conductivity to spatially inhomogeneous perturbations of the metric; we mainly focus on contributions that are secondorder in wavevector. 
Monday, March 5, 2018 1:03PM  1:15PM 
B07.00010: Controlled Parity Switch of Persistent Currents in Quantum Ladders Michele Filippone, CharlesEdouard Bardyn, Thierry Giamarchi We investigate persistent currents for a fixed number of fermions in periodic quantum ladders threaded by AharonovBohm and transverse magnetic fluxes Φ and χ. We show that the coupling between ladder legs provides a way to effectively change the groundstate fermionnumber parity, by varying χ. We demonstrate that varying χ by 2π (one flux quantum) leads to an apparent fermionnumber parity switch. We find that persistent currents exhibit a robust 4π periodicity as a function of χ, despite the fact that χ→χ+2π leads to modifications of order 1/N of the energy spectrum, where N is the number of sites in each ladder leg. We connect the parity switching effect to the quantum Hall regime in twodimensional systems. We show that the parity switching effect is related to the parity of the number of filled Landau levels and that it inherits strong robustness against disorder in the HarperHofstadter quantum Hall regime. The parityswitching and the 4π periodicity effects are robust with respect to temperature and disorder and we outline potential physical realizations using Corbino disk geometries in solid state systems, quantum ladders with cold atomic gases and, for bosonic analogs of the effects, photonic lattices. 
Monday, March 5, 2018 1:15PM  1:27PM 
B07.00011: Topological chargepumping effects induced by bulk magnetic fluxes CharlesEdouard Bardyn, Michele Filippone, Thierry Giamarchi The Hall conductance of quantum Hall systems can be related to topological (Thouless) pumping according to Laughlin’s celebrated argument. In the conventional setting, topological charge pumping is induced by threading a AharonovBohm flux through the hole of the system in cylinder or Corbino disk geometry. Here, we explore the analog of topological pumping induced, instead, by the insertion of flux quanta through the bulk of the system. Focusing on the lowenergy edge physics in the general framework of ChernSimons theory, we discuss physical effects induced by this alternative type of pumping in the context of integer and fractional quantum Hall systems. Our construction provides an intuitive setting to understand known effects and explore new ones. In particular, we show that adding superconductivity to the picture allows us to recover the 4π Josephson effect of Majorana fermions and its generalizations to parafermions. 
Monday, March 5, 2018 1:27PM  1:39PM 
B07.00012: Multifractal Analysis of Dirac Fermions Coupled to Disordered Abelian Gauge Field in Curved Space Noah Charles, Ilya Gruzberg A recent paper by Gruzberg et al. [Phys. Rev. B 95, 125414] argued that a certain form of geometric disorder in models for the integer quantum Hall transition may change the universal critical properties of the transition. In the continuum this disorder is described by a fluctuating 2D metric. Motivated by this, we examine a related model of Dirac fermions coupled to random gauge potentials on an arbitrary twodimensional curved manifold of genus 0 with a fixed (nonfluctuating) metric. We consider the effects of Abelian gauge potential disorder on the averaged generalized inverse participation ratios, and find that their scaling with the system size is described by anomalous multifractal exponents Δ(q) = (g/π)q(q1), where g is the strength of the gauge disorder. This scaling does not depend on the metric of the manifold and is the same as that of the Dirac fermions in flat space. The result can be verified using both the replica trick and the supersymmetry method for disorder averaging over the gauge field. 
Monday, March 5, 2018 1:39PM  1:51PM 
B07.00013: Wave Function and Emergent SU(2) Symmetry in $\nu_T=1$ Quantum Hall Bilayer Biao Lian, Shoucheng Zhang We propose a trial wave function for the quantum Hall bilayer system of total filling factor $\nu_T=1$ at a layer distance $d$ to magnetic length $\ell$ ratio $d/\ell=\kappa_{c1}\approx1.1$, where the lowest charged excitation is known to have a level crossing. The wave function has twoparticle correlations which fit well with those in previous numerical studies, and can be viewed as a BoseEinstein condensate of free excitons formed by composite bosons and anticomposite bosons in different layers. We show the free nature of these excitons indicating an emergent SU(2) symmetry for the composite bosons at $d/\ell=\kappa_{c1}$, which leads to the level crossing in lowlying charged excitations. We further show the overlap between the trial wave function and the ground state of a small size exact diagonalization is peaked near $d/\ell=\kappa_{c1}$, which supports our theory. 
Monday, March 5, 2018 1:51PM  2:03PM 
B07.00014: Quantum Hall Charge Kondo Criticality Zhiqiang Bao, Fan Zhang The longthought charge Kondo effects have recently been experimentally realized in the quantum Hall regime. This experiment, supported by numerics, exemplifies the realization of twochannel Kondo state, a nonFermi Liquid, and its crossover to the onechannel counterpart, a Fermi liquid. Scaling up such a platform, we find a hierarchy of nonFermi Liquids and their tunable crossovers based on a renormalization group analysis. Utilizing results from a conformal field theory, we further examine the universal conductances of this strongly correlated system and their finite temperature scaling, which elucidate the sharp distinctions between charge and spin Kondo physics. Reference: arXiv:1708.09139, (2017). 
Monday, March 5, 2018 2:03PM  2:15PM 
B07.00015: Bosonization of a 2D Landau level Vladimir Zyuzin

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