Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F06: Exotic Transport Properties: Magnetoresistance, Quantum Hall, and Others |
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Sponsoring Units: DCMP Chair: Dmitrii Maslov, University of Florida Room: BCEC 109A |
Tuesday, March 5, 2019 11:15AM - 11:27AM |
F06.00001: Giant magnetoresistance in BaMn_{2}Pn_{2} (Pn = As, Sb, Bi) Khuong Huynh, Takuma Ogasawara, Stephane Yu Matsushita, Taimu Tahara, Takanori Kida, Masayuki Hagiwara, Denis Arcon, Katsumi Tanigaki We report our discovery of a new kind of giant magnetoresistance (GMR) in the family of BaMn_{2}Pn_{2} antiferromagnets, where Pn stands for As, Sb, and Bi [1, 2]. BaMn_{2}Pn_{2}’s are intriguing materials hosting a magnetic hexadecapole ordering that preserves the parity-time symmetry even though both time and space inversion are broken [3]. The hexadecapole ordering microscopically stems from symmetry-preserved spin-dependent d-p hybridization that governs the low energetic excitations and therefore promises exotic transport properties. Here we describe a new GMR in BaMn_{2}Pn_{2}’s with the following features [1,2]: (1) the magnitudes of the unique negative GMR are larger than 98 %, being comparable with those of other exotic GMR systems, (2) GMR exhibits a very unusual angular under the rotation of magnetic fields, (3) GMR is band selective in sign, showing negative and positive signs for hole- and electron-like carriers, respectively. These properties are incompatible to any known mechanism of magnetoresistance and call for new explanations. |
Tuesday, March 5, 2019 11:27AM - 11:39AM |
F06.00002: Hall effects in giant magnetoresistance system BaMn_{2}Bi_{2} Takuma Ogasawara, Khuong Huynh, Stephane Yu Matsushita, Taimu Tahara, Takanori Kida, Masayuki Hagiwara, Denis Arcon, Katsumi Tanigaki A new kind of giant magnetoresistance (GMR) is observed in the family of G-type antiferromagnets BaMn_{2}Pn_{2} ’s, where Pn denotes pnictide elements of As, Sb, and Bi. The -98% GMR appears intriguingly with an unique angular dependence under rotating magnetic fields [1, 2] on the background of a complex magnetic hexadecapole ordering that preserves the parity-time symmetry even though the parity and time reversal symmetries are broken respectively[3]. Among the BaMn_{2}Pn_{2} ’s , BaMn_{2}Bi_{2} shows the largest MR in the smallest magnetic field range and therefore is the key material of the BaMn_{2}Pn_{2} family [1] for further detailed studies. We have measured the angular dependence of magnetoresistance and Hall effect of BaMn_{2}Bi_{2} to investigate the effect of magnetic field on the electrical conductivity. The results of our analyses suggest that the observed GMR stems from a large enhancement in the mobility of hole-like carriers induced by magnetic fields. |
Tuesday, March 5, 2019 11:39AM - 11:51AM |
F06.00003: Effect of Chemical Substitutions on the Extreme Magnetoresistance and Topological State of PtSn_{4} Alannah Hallas, Chien-Lung Huang, Emilia Morosan It has recently been discovered that the extreme magnetoresistive material PtSn_{4} [1] has a novel topological state, with the observation of Dirac node arcs in ARPES measurements [2]. This material has a quasi-two dimensional crystal structure composed of an edge-sharing network of PtSn_{8}-square antiprisms. We study the effect of chemical substitutions on the electronic properties of PtSn_{4} via two pathways: (i) we consider the effect of replacing platinum by gold, giving AuSn_{4} and (ii) we consider the effect of substituting tin with lead, giving PtPb_{4}. In the first substitution the crystallographic properties are left unaltered (ABAB stacking, orthorhombic) but in the second there is a minor structural modification (AAA stacking, tetragonal). Both materials superconduct at low temperatures with T_{c} = 2.5 K for AuSn_{4} and T_{c} = 2.8 K for PtPb_{4}. In this talk, we will present our studies of the electronic and topological properties of these compounds and comment on their relationship to PtSn_{4}. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F06.00004: Charge transport in doped SrTiO_{3} Abhishek Kumar, Dmitrii Maslov Recent experiments identified an unusual T^{2} dependence of the resistivity in doped strontium titanate (SrTiO_{3}). That this dependence is observed even at low doping, when umklapps are essentially impossible, and at temperatures far exceeding the Fermi energy eliminates electron-electron interaction as a possible source of the T^{2} resistivity. The T^{2} term may come from the interaction of electrons with two soft transverse optic (TO) phonons, characteristic for this material (the Epifanov-Levanyuk-Levanyuk mechanism). However, it is unclear within this model why the T^{2} term would be observed at temperatures smaller than the TO phonon frequency. We show that this behavior can be understood within a model in which the TO frequency varies over the sample from a larger value, observed in neutron and Raman scattering experiments, to a smaller value. A mictroscopic justification of this model relies on the experimentally observed polar boundaries between antiphase domains. Within the same model, we showed that the next-order correction to T^{2} term is T^{6} which is due to interaction of electrons with four TO phonons. Therefore, the TO phonon scattering is not able to explain the T^{3} behavior of the resistivity observed at higher temperatures. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F06.00005: Boundary layer theory for quantum Hall hydrodynamics Sriram Ganeshan, Alexander Abanov, Tankut Can, Gustavo M Monteiro In this talk, we consider non-dissipative two-dimensional broken parity fluids with odd viscosity and magnetic field with a free surface boundary condition. We show that for non-dissipative fluids, incompressibility must be violated at free surfaces to have a consistent hydrodynamic description of the dynamical boundary. Violation to incompressibility sources vorticity within the boundary layer which is an exclusive manifestation of odd viscosity. The thickness of the boundary layer is controlled by the velocity of sound. A non-dissipative boundary layer mechanism allows us to write the full variational principle for both bulk and boundary. In the limit of large sound velocity, we recover Quantum Hall like fluids where the bulk is incompressible but the thin boundary layer manifests compression modes. We discuss the applicability of our results to (fractional) quantum Hall fluids with a free surface. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F06.00006: Dynamics of the Phase Separated States in the Double Exchange Model Jing Luo, Gia-Wei Chern We present large-scale simulations of spin dynamics in the phase-separated states of the one-orbital double-exchange model. These inhomogeneous electronic states consisting of ferromagnetic conducting clusters embedded in an antiferromagnetic insulating background play a crucial role in the colossal magnetoresistance phenomenon. We compute the dynamical structure factor of these nanoscale textures using an efficient real-space formulation of coupled spin and electron dynamics. Dynamical signatures of the various underlying magnetic correlations are identified. At small hole doping, the structure factor exhibits a dominating signal of magnons from the background N\'eel order and localized modes from small metallic clusters. A low-energy continuum due to large-size ferromagnetic clusters emerges at higher doping levels. Implications for experiments on magnetoresistive manganites are also discussed. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F06.00007: Detecting fractional Chern insulators through circular dichroism Cecile Repellin, Nathan Goldman Great efforts are currently devoted to the engineering of topological Bloch bands in cold atomic gas. Recent achievements in this direction as well as the possibility of tuning inter-particle interactions suggests that strongly-correlated states reminiscent of fractional quantum Hall (FQH) liquids, could soon be generated in these atomic systems. In this context where transport measurements are limited, identifying unambiguous signatures of FQH-like states constitutes a challenge on its own. Here, we demonstrate that the fractional nature of the quantized Hall conductance, a fundamental characteristic of FQH states, could be finely detected in ultracold gases through a circular-dichroic measurement, namely by measuring the energy absorbed by the atomic cloud upon a circular drive. We discuss how such measurements, which were recently implemented in the integer-QH regime, could indeed be performed to distinguish FQH-type states from competing states (such as charge density waves). Our scheme offers a practical and powerful tool for the detection of topological order in quantum engineered systems. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F06.00008: Bridging Hubbard Model Physics and Quantum Hall Physics in ABC Trilayer Graphene/h-BN moir\'e superlattice Yahui Zhang, Senthil Todadri Recently several phases resulting from electron correlations have been discovered in graphene moire superlattice with narrow bands. In this talk I will focus on the moire superlattice formed by ABC stacked trilayer graphene aligned with a hexagonal boron nitride substrate (TG/h-BN). Mott-like insulators in this system have already been observed experimentally by Feng Wang et.al. (Chen, Feng Wang et.al. arxiv: 1803.01985). Remarkably, in TG/h-BN, both the bandwidth and the topology can be tuned by an applied perpendicular electric field D . For D<0, the valence bands of the two valleys are trivial and the physics is governed by a spin-valley Hubbard model on triangular lattice. For D>0, the bands of the two valleys have non-zero Chern numbers C=3,-3. Therefore the TG/h-BN system can simulate both Hubbard model physics and nearly flat Chern band physics within one sample through a simple switch of the vertical displacement field. I am going to discuss several aspects of the resulting many body physics. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F06.00009: Non-Abelian quasiholes in lattice Moore-Read states and parent Hamiltonians Julia Wildeboer, Sourav Manna, German Sierra, Anne E. B. Nielsen A striking feature of fractional quantum Hall states is that they form an incompressible quantum state |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F06.00010: Theory of magnon transport in quantum Hall ferromagnet Chunli Huang, Allan MacDonald In two recent experiments, Stepanov et. al [Nat. Phys 14, 907–911 (2018)] and Wei. et al [Science 362, 6411, 229-233 (2018)] observed long distance, nonlocal magnon transport in quantum Hall magnetic states of graphene. In these experiments, bulk magnons are excited in close proximity to conducting spin polarized edge states that are under external voltage bias. While Stepanov et. al observed a nonlocal voltage linear in the bias voltage, Wei. et al observed a nonlocal voltage only when within a window of bias voltage that begins at Zeeman energy. Motivated by these observations, we present a simple theoretical model to study edge-current induced torque -- the coupled dynamics of itinerant spin-polarized edge states and insulating bulk magnons. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F06.00011: Effective field theory of a vortex lattice in a bosonic superfluid Sergej Moroz, Carlos Hoyos, Claudio Benzoni, Dam Thanh Son Using boson-vortex duality, we formulate a low-energy effective theory of a two-dimensional vortex lattice in a bosonic Galilean-invariant compressible superfluid. The excitation spectrum contains a gapped Kohn mode and an elliptically polarized Tkachenko mode that has quadratic dispersion relation at low momenta. External rotation breaks parity and time-reversal symmetries and gives rise to Hall responses. We extract the particle number current and stress tensor linear responses and investigate the relations between them that follow from Galilean symmetry. We argue that elementary particles and vortices do not couple to the spin connection which suggests that the Hall viscosity at zero frequency and momentum vanishes in a vortex lattice. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F06.00012: Electronic Spectral functions, ρ(T) and Raman response in the 2-d t-J model Peizhi Mai, B Shastry We study the two-dimensional t-J model with a second neighbor hopping parameter t', in a broad range of doping δ using a closed set of equations from the Extremely Correlated Fermi Liquid (ECFL) theory. The electronic spectral function is found to yield asymmetric energy distribution curves and symmetric momentum distribution curves. These are broadly consistent with experimental data. Using our spectral functions, we calculate the resistivity, whose curvature changes with varying δ is presented, and connect this change to the intensity loss in Angle-Resolved Photoemission Spectroscopy (ARPES) experiments. We also present results for a set of closely related dynamical response functions: the non-resonant Raman susceptibility for three principal geometries germane to the square lattice, and the optical conductivity. Where available, these results are in close correspondence to available high-resolution experimental results. Our results provide a set of testable predictions for future experiments. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F06.00013: Transport, multifractality and breakdown of single-parameter scaling in quasiperiodic systems. Jagannath Sutradhar, Subroto Mukerjee, Rahul Pandit, Sumilan Banerjee We study the transport in 1d Aubry-Andre model, and its generalizations to 2d and 3d, which show significant deviations from single-parameter scaling theory providing a broad demarcation between QPS and RS. We study the conductance of open systems connected to leads as well as the Thouless conductance. Depending on dimension, the conductances show metal-insulator transition from localized to either ballistic, superdiffusive or diffusive transport typically through subdiffusive critical states. We show that, even though a beta function, β(g) =dln(g)/dln(L), can be constructed separately for individual phases based on a overall length (L) dependence of typical dimensionless conductance g, in 1d and 2d, the single-parameter scaling is unable to describe the transition. Moreover, the conductances show strong non-monotonic variations (multifractal scaling in 1d) with system size and intricate resonant peak and subpeak structures of number theoretic origin, invalidating a strict definition of β(g). We show that the non-monotonicity is very weak in 3d with a critical point having localization length exponent close to that of 3d Anderson transition and the single-parameter scaling is almost restored providing a good description of the metal-insulator transition. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F06.00014: Pairing correlations in the incoherent phase of quantum Hall bilayers? James Eisenstein, Loren Pfeiffer, Kenneth West At sufficiently small layer separation, Coulomb interactions in bilayer 2D electron systems at high magnetic field can stabilize an excitonic phase in which electrons in one layer are bound to holes in the other. The excitonic phase is macroscopically phase coherent, exhibiting numerous remarkable transport properties analogous to those of superconductivity and superfluidity. While the excitonic phase is theoretically relatively well understood, the incoherent phase at layer separations slightly larger than the critical one is not. In this talk we will discuss recent transport and interlayer tunneling spectroscopy measurements which demonstrate the importance of interlayer Coulomb interactions in the incoherent phase. In addition to screening of the Coulombic repulsion between electrons in the same layer, our measurements suggest that interlayer electron-hole pairing correlations may persist into the incoherent phase at intermediate layer separations. |
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