Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X01: Integer Quantum Hall Effect |
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Sponsoring Units: DCMP Room: BCEC 106 |
Friday, March 8, 2019 8:00AM - 8:12AM |
X01.00001: Landau Velocity for Collective Quantum Hall Breakdown in Bilayer Graphene Holger Graef, Wei Yang, Xiaobo Lu, Guangyu Zhang, Takashi Taniguchi, Kenji Watanabe, Adrian Bachtold, Edwin Hang Tong Teo, Emmanuel Baudin, Erwann Bocquillon, Gwendal Fève, Jean-Marc Berroir, David Carpentier, Mark Oliver Goerbig, Bernard Plaçais Breakdown of the integer quantum Hall effect (QHE) is associated with an electric field approaching the inter-Landau-level (LL) Zener field, ratio of the Landau gap and the cyclotron radius. The intrinsic Zener limit, corresponding to critical drift velocity, is reported here [1] using high-mobility bilayer graphene and high-frequency shot noise [2] over a large number of LLs. The steep onset of shot noise at breakdown, exhibiting super-Poissonian Fano factors, shows that collective excitations arising from electron-electron interactions are essential. The breakdown mechanism can be described by a Landau critical velocity limited by the excitation of large momentum magneto-excitons, in analogy with the roton mechanism of superfluids [3]. The fractional QHE counterpart would involve magneto-rotons [4]. |
Friday, March 8, 2019 8:12AM - 8:24AM |
X01.00002: Stabilizing a SQUID-based amplifier in high magnetic fields Vidhi Shingla, Ethan Kleinbaum, Loren Pfeiffer, Kenneth West, Gabor Csathy dc SQUID-based circuits, when connected to sources exposed to strong magnetic fields, are often unstable in their fluxed-locked mode. We present a low noise SQUID-based current amplifier, which is unconditionally stable with a source exposed to magnetic fields up to 10 T. |
Friday, March 8, 2019 8:24AM - 8:36AM |
X01.00003: Andreev reflection at the interface with an oxide in the quantum Hall regime Yusuke Kozuka, Atsushi Sakaguchi, Joseph Falson, Atsushi Tsukazaki, Masashi Kawasaki Quantum Hall/superconductor junctions have been an attractive topic as the two macroscopically quantum states join at the interface. Despite longstanding efforts, most semiconductors hosting high-mobility two-dimensional electron systems (2DES) usually form Schottky barriers at the metal contacts, preventing efficient proximity between the quantum Hall edge states and Cooper pairs. In this study, we propose another material system for investigating 2DES/superconductor junctions, that is ZnO-based heterostrcuture. Due to the ionic nature of ZnO, a Schottky barrier is not effectively formed at the contact with a superconductor MoGe, as evidenced by the appearance of Andreev reflection at low temperatures. With applying magnetic field, while clear quantum Hall effect is observed for ZnO 2DES, conductance across the junction oscillates with the filling factor of the quantum Hall states. We find that Andreev reflection is suppressed in the well-developed quantum Hall regimes, which we interpret as a result of equal probabilities of normal and Andreev reflections as a result of multiple Andreev reflection at the 2DES/superconductor interface. |
Friday, March 8, 2019 8:36AM - 8:48AM |
X01.00004: Graphene in a Uniform Magnetic Field Ankur Das, Ribhu Kaul, Ganpathy N Murthy We study monolayer graphene in a uniform magnetic field in the absence and presence of interactions. In the non-interacting limit for 1/q flux quanta per unit cell, the central two bands have 2q Dirac points in the Brillouin zone for nearest neighbor hopping. The Dirac points can be gapped out with a 2nd nearest neighbor hopping (t2) and the central two bands pick up large Chern numbers. If we break the inversion symmetry by introducing a staggered potential (m) Chern number of the central bands becomes 1. Competition between t2 and m leads to a topological phase transition. |
Friday, March 8, 2019 8:48AM - 9:00AM |
X01.00005: Edge excitations in the 2D electron gas at ν=2 Amartya Saha, Ganpathy N Murthy Edge reconstruction for the 2D electron gas in a magnetic field at ν=2 has been studied by Dempsey, Gelfand, and Halperin[1], who found that when the confining potential is softened the two spin polarized channels spatially separate. In this project we study the collective excitations both in the bulk and the edge at ν=2 using the time dependent hartree fock ( TDHF) method. We find that beyond a certain slope of the edge potential both the spin-wave and the charged excitations have instabilities. This analysis is similar to what Franco and Brey[2] did for the ν=1 edge, where they showed that there are other phases (spin textured and charge density wave) with lower energy than the earlier proposed stripe phase by Chamon and Wen[3]. Finally, we will look for translation-symmetry-breaking ground states with lower energy than the one proposed in ref. 1 using Hartree-Fock methods. |
Friday, March 8, 2019 9:00AM - 9:12AM |
X01.00006: Boundary critical behavior of the integer quantum Hall transition Martin Puschmann, Philipp Cain, Michael Schreiber, Thomas Vojta We recently performed a high-accuracy study of the integer quantum Hall transition for a microscopic model of non-interacting disordered electrons: Based on a recursive Green function approach, we investigated the electronic wave functions in the lowest Landau band of a tight-binding model on a simple square lattice. To determine the bulk critical behavior, we employed lattices with the topology of an infinite cylinder [1]. |
Friday, March 8, 2019 9:12AM - 9:24AM |
X01.00007: Black Hole Phenomena in Quantum Hall Systems 1: Quasinormal Modes Varsha Subramanyan, Suraj Hegde, Smitha Vishveshwara, Barry Bradlyn Point contact geometries in quantum Hall systems have formed excellent probes of quasiparticle scattering. Here, we demonstrate how they can access quasinormal modes – temporally decaying excitations – which are hitherto unexplored in QH settings. On the astronomical scale, quasinormal modes are one of the characteristic signatures of black holes and have played a key role in the recent LIGO detection of black hole mergers. We show how lowest Landau level physics in the presence of a saddle potential, such as at a point contact, can directly simulate the scattering of scalar particles by a black hole spacetime. The S matrix obtained from this scattering problem has poles in the complex plane corresponding to the quasinormal modes. We present the results of Gaussian wavepacket scattering to discern these states in the reflected wavepacket. We also discuss the possible signatures of the quasinormal modes in time-resolved measurements on quantum Hall systems in point contact geometries. |
Friday, March 8, 2019 9:24AM - 9:36AM |
X01.00008: Black Hole phenomena in Quantum Hall Systems 2: The Hawking-Unruh effect Suraj Hegde, Varsha Subramanyan, Barry Bradlyn, Smitha Vishveshwara In this talk, we present a parallel between dynamics in quantum Hall systems and the Hawking-Unruh effect associated with black holes. Hawking-Unruh radiation can be looked upon as a thermal distribution that arises from a Bogoliubov transformation generated by the Rindler Hamiltonian, corresponding to accelerated observers. We show that the Rindler Hamiltonian is functionally identical to that of Hamiltonian governing electrons in the lowest Landau level in the presence of a saddle potential. We show that this arises from a deeper connection between the symmetries of the two disparate systems – the isomorphism between the lie algebras of the 2+1D Lorentz group and that of SL(2,R) group of area- preserving transformations. This connection further allows us to see quantum Hall phenomena in the light of Lorentz kinematics. |
Friday, March 8, 2019 9:36AM - 9:48AM |
X01.00009: Quantum tomography of electrical currents REMI BISOGNIN, Benjamin Roussel, Camille Chapdelaine, Arthur Marguerite, Manohar Kumar, Cl�ment Cabart, Ali Mohammed-Djafari, Jean-Marc Berroir, Erwann Bocquillon, Bernard Plaçais, Antonella Cavanna, Ulf Gennser, Young Jin, Pascal Degiovanni, Gwendal Fève Recent developments in quantum nanoelectronics have enabled the realization of electron sources emitting a quantized number of excitations. However, reconstructing all wavefunctions of the elementary excitations embedded in electrical currents was still out of reach. |
Friday, March 8, 2019 9:48AM - 10:00AM |
X01.00010: QED-Bloch Theory with Homogeneous Magnetic Fields: Modifications of the Landau Levels and the Hofstadter Butterfly Vasil Rokaj, Markus Penz, Michael Sentef, Michael Ruggenthaler, Angel Rubio Probing electronic properties of periodic systems by arbitrary homogeneous magnetic fields has |
Friday, March 8, 2019 10:00AM - 10:12AM |
X01.00011: A Topological Sum-Rule Causes the Total Suppression of the Hall Response Michele Filippone, Charles-Edouard Bardyn, Sebastian Greschner, Thierry Giamarchi We present a topological sum-rule for the transverse polarization valid for out-of-equilibrium quantum states in two-dimensional lattices. Whenever the state equally spreads over all bands at a fixed energy, the topological sum-rule implies the identical suppression of the polarization, regardless of the magnetic field strength. As a remarkable consequence, the Hall response robustly vanishes even in absence of particle-hole symmetry and with arbitrary strong magnetic fields. We show that these out-of-equilibrium states are commonly realized in standard (Landauer) quantum transport settings and we rely on DMRG to show that our results equally apply to strongly interacting regimes. |
Friday, March 8, 2019 10:12AM - 10:24AM |
X01.00012: Andreev edge state in the quantum Hall regime Lingfei Zhao, Ethan Arnault, Andrew Seredinski, Anne M Draelos, Hengming Li, Tate Fleming, brandon bell, Kenji Watanabe, Takashi Taniguchi, Francois Amet, Gleb Finkelstein We investigate Andreev reflections in the quantum Hall regime. We study an encapsulated graphene sample contacted by both superconducting and normal electrodes. In the well-quantized regime, we find evidence for Andreev reflections of the QH edge states traveling along the superconducting contacts. The observed spectroscopic features decay to zero with increasing temperature and magnetic field. We attribute them to beating between electron-hole modes hybridized by Andreev reflections. These chiral modes under certain conditions are predicted to be Majorana-Weyl fermions. |
Friday, March 8, 2019 10:24AM - 10:36AM |
X01.00013: Interacting quantum Hall states at integer filling with a non-Abelian twist: a coupled wire description Pedro Lopes, Victor Quito, Bo Han, Jeffrey Teo We construct a theoretical coupled wire model that describes new many-body interacting quantum Hall states at integer filling. The strongly-correlated states support exotic electric and thermal Hall transport that violate the Wiedemann-Franz law ν/c=(σxy/κxy)[π2kB2/(3e2)]T>1. We focus on strongly-paired states where combinations of pairs of electrons form the fundamental interacting constituents. These bosonic combinations associate to a Kac-Moody current algebra, which is removed from low-energy by the interaction in the 2+1D bulk but is left behind along the 1+1D boundary. We propose a new quantum Hall state at filling ν=16 that supports a bosonic chiral E8 edge current algebra at level 1 and is intimately related to the topological paramagnets in 3+1D. This topological state can be partitioned into two quantum Hall states at filling ν=8, each carries a bosonic chiral G2 or F4 edge current algebra at level 1 and hosts non-Abelian Fibonacci anyonic excitations in the bulk. Moreover, we discover a new notion of particle-hole conjugation, based on the E8 bosons, that switches between the G2 and F4 states. |
Friday, March 8, 2019 10:36AM - 10:48AM |
X01.00014: Filling-enforced quantum oscillation phase shift anomaly in few-layer graphene Biswajit Datta, Pratap Chandra Adak, Li-kun Shi, Kenji Watanabe, Takashi Taniguchi, Justin Song, Mandar Deshmukh Quantum oscillations provide a striking visualization of the Fermi surface of metals: Fermi surface size, shape, and Berry phase naturally manifest in quantum oscillation frequency, field-direction dependence, and phase shift respectively. We report on unconventional magneto-transport of ABA-trilayer graphene, a multiband system comprising a (non-trivial) gapped monolayer graphene (MLG)-like band, nested within a large (trivial) bilayer graphene (BLG)-like band. Detailed field and density maps reveal BLG-like Shubnikov-de Hass (SdH) oscillations shifted by an anomalous non-trivial phase that sharply departs from that expected from the constant and trivial (2π) Berry phase of the BLG-like Fermi surface. The anomalous phase shift switches sharply from π to – π as density is tuned from below the MLG-like gap to above it. This originates from a strong filling-enforced constraint between the BLG-like and MLG-like Fermi surfaces, enabling the quantum oscillations of one Fermi surface to inherit the phase shifts of the other co-existing Fermi surface. We expect filling-enforced phases in quantum oscillations to arise generically in multi-Fermi-surface metals, and provide a detailed window to map the rich pattern of carrier filling in multi-band topological materials. |
Friday, March 8, 2019 10:48AM - 11:00AM |
X01.00015: Taming electronic decoherence in 1D chiral ballistic conductor Clement Cabart, Benjamin Roussel, Gwendal Fève, Pascal Degiovanni Decoherence and relaxation of single-electron excitations induced by strong effective screened Coulomb interactions in Quantum Hall edge channels are an important challenge for the applications of electron quantum optics in quantum information and quantum sensing. We present a complete study of intrinsic single-electron decoherence within an ideal single-electron channel with long-range effective Coulomb interactions to determine the influence of the material and sample properties [Phys. Rev. B 98, 155302 (2018)]. We find that weak-coupling materials characterized by a high velocity of hot-electron excitations such as graphene may offer interesting perspectives for limiting intrinsic decoherence due to electron/electron interactions compared to lower velocity materials such as AlGaAs/AsGa. We discuss quantitively how extrinsic decoherence due to the coupling with the channel's electromagnetic environment can be efficiently inhibited in specifically designed samples at filling fraction two with one closed edge channel and we propose a realistic geometry for testing decoherence control in a Hong Ou Mandel experiment. |
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