Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F27: Semiconductors and the Hall Effect II. |
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Sponsoring Units: FIAP Chair: Ali Yazdani, Princeton University Room: 290 |
Tuesday, March 14, 2017 11:15AM - 11:27AM |
F27.00001: Observation of a nematic quantum Hall liquid on the surface of bismuth Benjamin E. Feldman, Mallika T. Randeria, Andras Gyenis, Fengcheng Wu, Huiwen Ji, Robert J. Cava, Allan H. MacDonald, Ali Yazdani Nematic quantum fluids with wavefunctions that break the underlying crystalline symmetry can spontaneously form as a result of electronic correlations. We examine the quantum Hall states that arise in high magnetic fields from anisotropic hole pockets on the Bi(111) surface. Spectroscopy performed with a scanning tunneling microscope shows that a combination of local strain and exchange interactions lift the six-fold Landau level degeneracy to form three valley-polarized quantum Hall states. We image the resulting anisotropic wavefunctions and show that they have a different orientation for each broken-symmetry state. Our measurements provide a direct spatial signature of a local domains of a nematic quantum Hall liquid. Moreover, this is the first material system where the role of electronic interactions in the formation of nematic order can be quantified and directly correlated with a microscopic theory. [Preview Abstract] |
Tuesday, March 14, 2017 11:27AM - 11:39AM |
F27.00002: Imaging individual Landau Level wavefunctions on the surface of bismuth Mallika T. Randeria, Benjamin E. Feldman, Andras Gyenis, Hao Ding, Fengcheng Wu, Huiwen Ji, Robert J. Cava, Allan H. MacDonald, Ali Yazdani The scanning tunneling microscope (STM) is a powerful tool to image electronic wavefunctions with high energy and spatial resolution. We examine the quantum Hall states that arise in a high magnetic field from anisotropic hole pockets on the Bi(111) surface. Spectroscopic mapping performed with a STM at the energies of valley-polarized Landau levels show elliptical rings of suppressed conductance centered on atomic-scale surface defects. These rings correspond to individual cyclotron orbits whose energy has been shifted by the defect potential and the overall shape matches well to the expected Landau orbits. Our measurements also reveal finer features of the wavefunction, which point to physics not captured by this simple analysis. We will discuss this aspect of the data and a possible interpretation within the framework of a more comprehensive model. In addition to providing the first direct mapping of isolated cyclotron orbits, this technique has the potential to visualize other exotic quantum wavefunctions on the atomic scale. [Preview Abstract] |
Tuesday, March 14, 2017 11:39AM - 11:51AM |
F27.00003: Imaging domain walls between nematic quantum Hall phases on the surface of bismuth Hao Ding, Mallika T. Randeria, Benjamin E. Feldman, Huiwen Ji, Robert J. Cava, Ali Yazdani The sensitivity of nematic electronic phases to disorder results in short range ordering and the formation of domains. Local probes are required to investigate the character of these domains and the boundaries between them, which remain hidden in global measurements that average over microscopic configurations. In this talk, I will describe measurements performed with a scanning tunneling microscope to study local nematic order on the surface of bismuth at high magnetic field. By imaging individual anisotropic cyclotron orbit wavefunctions that are pinned to atomic-scale surface defects, we directly resolve local nematic behavior and study the evolution of nematic states across a domain wall. Through spectroscopic mapping, we explore how the broken-symmetry Landau levels disperse across the domain wall, the influence of exchange interactions at such a boundary, and the formation of one-dimensional edge states. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F27.00004: Surface Transport and Quantum Hall Effect in Ambipolar Black Phosphorus Double Quantum Wells Jiawei Yang, Son Tran, Nathaniel Gillgren, Timothy Espiritu, Yanmeng Shi, Kenji Watanabe, Takashi Taniguchi, Seongphill Moon, Hongwoo Baek, Dmitry Smirnov, Marc Bockrath, Ruoyu Chen, Chun Ning Lau Quantum wells (QWs) is the most important class of devices in the study of two-dimensional (2D) systems. Here we demonstrate facile formation of black phosphorus-based wide QWs that host double layers of charge carriers. In contrast to tradition QWs, each 2D layer is ambipolar, and can be tuned into n-doped, p-doped or intrinsic regimes. Fully spin-polarized quantum Hall states are observed on each layer, with Land\'{e} $g$-factor that is attributed to exchange interactions. Our work opens the door for using 2D semiconductors as ambipolar single, double or wide QWs with unusual properties such as high anisotropy. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F27.00005: Landau level gaps in high mobility black phosphorus devices Son Tran, Jiawei Yang, Jason Wu, Hongwoo Baek, Dmitry Smirnov, Takashi Taniguchi, Kenji Watanabe, Ruoyu Chen, Chun Ning Lau Black phosphorus (BP) has recently attracted wide interest as a high mobility two-dimensional semiconductor. Here we report encapsulated few-layer BP field effect transistors achieving high field effect mobility at cryogenic temperatures and observation of the integer quantum Hall effect in high magnetic field. We examine the devices' anisotropic transport properties and the Landau level gaps by varying temperature and magnetic field. Latest results will be discussed and compared with theoretical models. [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F27.00006: Unusual temperature dependence of quantum Hall stripes in ultra-high quality AlGaAs/GaAs two-dimensional electron gases Michael Manfra, Qi Qian, James Nakamura, Saeed Fallahi, Geoffrey Gardner We report a temperature dependence study of anisotropic electron transport in high (N $=$ 2, 3) Landau levels in an ultra-high quality AlGaAs/GaAs two-dimensional electron system. At half filling, the magnetoresistance along the easy direction drops to zero at low temperature and remains zero as temperature is decreased further, while along the hard direction it reaches a peak at intermediate temperature and then decreases as temperature is lowered all the way down to the base temperature of our dilution refrigerator (10mK). At low temperature, time-dependent fluctuations in longitudinal resistance become substantial and hysteresis is observed in magnetic field sweeps through $\nu =$9/2, 13/2 and 15/2. The temperature dependence of the anisotropic resistance at each half filling suggests that we are possibly observing a nascent phase transition from quantum Hall stripes to a Wigner solid at the lowest temperatures. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F27.00007: Electrostatic and Quantum Transport Simulations of Quantum Point Contacts in the Integer Quantum Hall Regime Harshad Sahasrabudhe, Saeed Fallahi, James Nakamura, Michael Povolotskyi, Bozidar Novakovic, Rajib Rahman, Michael Manfra, Gerhard Klimeck Quantum Point Contacts (QPCs) are extensively used in semiconductor devices for charge sensing, tunneling and interference experiments. Fabry-P\'{e}rot interferometers containing 2 QPCs have applications in quantum computing, in which electrons/quasi-particles undergo interference due to back-scattering from the QPCs. Such experiments have turned out to be difficult because of the complex structure of edge states near the QPC boundary. We present realistic simulations of the edge states in QPCs based on GaAs/AlGaAs heterostructures, which can be used to predict conductance and edge state velocities. Conduction band profile is obtained by solving decoupled effective mass Schr\"{o}dinger and Poisson equations self-consistently on a finite element mesh of a realistic geometry. In the integer quantum Hall regime, we obtain compressible and in-compressible regions near the edges. We then use the recursive Green`s function algorithm to solve Schr\"{o}dinger equation with open boundary conditions for calculating transmission and local current density in the QPCs. Impurities are treated by inserting bumps in the potential with a Gaussian distribution. We compare observables with experiments for fitting some adjustable parameters. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F27.00008: Optical Radiation from Integer Quantum Hall States in Dirac Materials Michael Gullans, Jacob Taylor, Pouyan Ghaemi, Mohammad Hafezi Quantum Hall systems exhibit topologically protected edge states, which can have a macroscopic spatial extent. Such edge states provide a unique opportunity to study a quantum emitter whose size far exceeds the wavelength of emitted light. To better understand this limit, we theoretically characterize the optical radiation from integer quantum Hall states in two-dimensional Dirac materials. We show that the scattered light from the bulk reflects the spatial profile of the wavefunctions, enabling spatial imaging of the disorder landscape. We find that the radiation from the edge states are characterized by the presence of large multipole moments in the far-field. This multipole radiation arises from the transfer of angular momentum from the electrons into the scattered light, enabling the generation of coherent light with high orbital angular momentum. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F27.00009: Generic Hall viscosity and response functions in the IQHE Yu Shen, F. D. M. Haldane We reformulate the Hall viscosity for the IQHE in the most generic case without rotational or Galilean symmetry. By defining the stress-energy tensor as the response to strain of the matter fields rather than to variation of the metric (which doesn't exist at the absence of rotational symmetry), we differentiate between covariant and contravariant indices to clarify the structure of the tensor. Generic density/current response functions are also calculated. The simple identification of the $q^2$ term of the Hall conductance as the Hall viscosity breaks down and we show that the $q^2$ term consists of a universal part that is proportional to the Hall viscosity tensor and other non-universal Landau-level-mixing terms that depend on the details of the Hamiltonian. In the Galilean limit, the formula reduces to the previously found form. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F27.00010: Effect of alloy disorder on quantum Hall stripes Q. Shi, M. Zudov, J. Watson, G. Gardner, M. Manfra It is widely believed that quantum Hall stripes are best observed in very clean GaAs samples. However, the role of disorder on stripes has not been systematically studied and remains poorly understood. Here, we report studies on the impact of alloy disorder, controlled by the aluminum content $x$ in the Al$_{x}$Ga$_{1-x}$As channel ($x$ = 0 – 0.0078), in a series of otherwise similar quantum wells. We investigate how alloy disorder affects the low temperature transport, as well as the melting transition of stripes at elevated temperatures, and compare them to the bubble phases. We also discuss the impact of alloy disorder on the reorientation of stripes by an in-plane magnetic field. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F27.00011: Band structure in bulk entanglement spectrum of quantum Hall state Chi-Ken Lu, D.-W. Chiou, F.-L. Lin We study the bulk entanglement spectrum of integer quantum Hall state with a symmetric checkerboard partition of space. By reformulating the correlation matrix in a guiding center representation, we show that the problem is mapped to a two-dimensional lattice with unit vector determined by the field and partition grid. The bulk entanglement spectrum shows the particle-hole symmetry and the band touching, whic are related to the dual symmetry of partition and the Chern number, respectively. Ref. 1 T. Hsieh and L. Fu, PRL 113, 106801 (2014). Ref. 2 Q. Zhu, X. Wan, and G.-M. Zhang, PRB 90 235134 (2014). Ref. 3 C.-K. Lu, D. Chiou, and F. Lin PRB 92 075130 (2015). [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F27.00012: SU(4) quantum Hall skyrmions in graphene in the quarter-filled N=0 Landau level Yunlong Lian, Mark-Oliver Goerbig, Achim Rosch Skyrmions are present in multi-component quantum Hall systems where the splittings of Landau sub-levels are small compared to the Coulomb energy. Using a minimal field theory obtained by a variational approach, we study various types of charge-1 skyrmions in the vicinity of the quarter-filled N=0 Landau level of graphene. We find novel texture states in the spin-pseudospin-entanglement channel, as well as the transitions between phases corresponding to different skyrmion types [1]. 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 multi-component quantum Hall systems. [1] Lian et al., PRL 117,056806(2016) [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F27.00013: Wigner function of a quantum Hall edge channel excited at GHz frequency Arthur Marguerite, Clément Cabart, Jean Marc Berroir, Bernard Plaçais, Yong Jin, Antonella Cavanna, Gwendal Fève In the rapidly evolving field of quantum computing, tremendous efforts have been made to realize phase-coherent electronics in the hope to process quantum information encoded on the electronic degrees of freedom. It is now possible to create and propagate quantum states with finite temporal and energy extensions. Although differential conductance or current fluctuations enable to recover energy distribution averaged in time of these states, it does not permit a complete reconstruction of a quantum state. To access, for instance, its Wigner distribution one needs a tomography protocol. We will present the implementation of such a protocol in a 2 dimensional electron gas in the regime of integer quantum Hall effect where the 4 terminals geometry allows to separate the source from the probe. Although the protocol is fully universal, we tested it on an edge channel excited with a sinusoidal drive. This creates a many excitations state that, for hf > kT, differs from a simple Fermi sea with a time-varying chemical potential. Indeed, we were able to measure negativities in the Wigner function at a frequency drive of 9 GHz. This is a manifestation of photo-assisted transport which is quantized by nature. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F27.00014: Temperature-induced reorientation of quantum Hall stripes M. Zudov, Q. Shi, B. Friess, J. Smet, J. Watson, G. Gardner, M. Manfra We report observation of orthogonal orientations of quantum Hall stripes detected in magnetoresistance measured at different temperatures in a high-quality GaAs quantum well with the magnetic field tilted slightly away from the sample normal. Despite non-hysteretic magnetoresistance at low and high temperatures, field-cooling at a fixed filling factor close to $\nu =$ 9/2 and observation of hysteresis at intermediate temperatures allow us to conclude that the stripes orientation at low temperature is metastable. These findings suggest that low-temperature magnetotransport data should be treated with caution as they do not necessarily reveal the true ground state, and that the native symmetry-breaking potential has a very weak temperature dependence. [Preview Abstract] |
Tuesday, March 14, 2017 2:03PM - 2:15PM |
F27.00015: Hydrodynamic Electron Flow and Hall Viscosity Thomas Scaffidi, Philip Moll, Pallavi Kushwaha, Nabhanila Nandi, Burkhard Schmidt, Andrew Mackenzie, Joel Moore In metallic samples of small enough size and sufficiently strong electron-electron scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory for which bounds on diffusion were conjectured based on an holographic correspondence. Furthermore, breaking time-reversal symmetry can lead to the appearance of an odd component to the viscosity called the Hall viscosity which has attracted a lot of attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields. [Preview Abstract] |
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