Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G37: DisorderDriven Transitions in Dirac Materials and Related SystemsInvited

Hide Abstracts 
Sponsoring Units: DCMP Chair: Leo Radzihovsky, University of Colorado, Boulder Room: 605 
Tuesday, March 3, 2020 11:15AM  11:51AM 
G37.00001: Highdimensional disorderdriven phenomena in nodal semimetals and systems with longrange hopping Invited Speaker: Sergey Syzranov Systems of noninteracting electrons are believed widely to exhibit only one type of disorderdriven transitions: the Anderson localisation transition. It has been suggested, however, that systems with the powerlaw quasiparticle dispersion k^{α} in high dimensions d>2α, exemplified by 3D Weyl and Dirac semimetals, may exhibit transitions in a different universality class, as well as unconventional energylevel statistics, Lifshitz tails and ballistictransport properties. In this talk, I will review existing results on the nonAnderson transitions and other unconventional disorderdriven phenomena in nodal semimetals and related systems (quantum kicked rotors, arrays of ultracold ions, 1D and 2D plasmonic systems, etc.). Also, I will demonstrate that the field theories of disordered nodal semimetals with α<d can be mapped exactly onto those of systems with longrange hopping of quasiparticles, where hopping decays with distance r slower than 1/r^{d} (trapped ultracold ions, spins in solids, nitrogen defects in diamonds, etc.). This duality allows to describe the properties of each of these two classes of systems using the results established for the other class and, in particular, establishes the existence of unconventional disorderdriven transitions in systems with longrange hopping. 
Tuesday, March 3, 2020 11:51AM  12:27PM 
G37.00002: Disordered Weyl Semimetals: From Lattice Models to the Continuum Invited Speaker: Jed Pixley We will discuss numerical studies of disordered Weyl semimetals focusing on the effects of rare regions at low energy. We will review our work on lattice models of Weyl semimetals which demonstrates the existence of rare region induced nonperturbative eigenstates, an exponentially small but nonzero density of states at the Weyl node, an exponentially large quasiparticle lifetime, and an avoided quantum critical point. We will then present our recent study of a single Weyl cone in the presence of shortrange disorder. To numerically handle the continuum we represent the Hamiltonian in a "mixed" way between real and momentum space so that we are able to invoke fast Fourier transforms to take advantage of efficient numerical routines (such as Lanczos and the kernel polynomial method) that rely on sparse matrixvector multiplications. As a result, we can reach sufficiently large system sizes that are comparable to our lattice model calculations. We will report results on the nature of rare regions and the density of states as a function of the strength of disorder and the ultra violet cut off, as well as compare and contrast singlenode and multinode results. In all of the cases studied, we will demonstrate that the putative semimetal to diffusive transition is rounded into a cross over. 
Tuesday, March 3, 2020 12:27PM  1:03PM 
G37.00003: Imaging the work, dissipation and topological protection in the quantum Hall state Invited Speaker: Arthur Marguerite Topology is a powerful concept asserting that quantum states can be globally protected against local perturbation. These states are of major fundamental interest as well as of practical importance in metrology and quantum information technology. However, topological protection in realistic devices it is often fragile against dissipative mechanisms, which are difficult to probe directly. Using scanning nanothermometry, we visualize microscopic mechanisms undermining the topological protection in the quantum Hall state in graphene. Our simultaneous nanoscale thermal and scanning gate microscopy reveals that the dissipation is governed by crosstalk between counterpropagating downstream and upstream channels that appear at graphene boundaries because of edge reconstruction. The dissipation mechanism comprises two distinct and spatially separated processes. The work generating process that we image directly and which involves elastic tunneling of charge carriers between the quantum channels, determines the transport properties but does not generate local heat. The heat generating process, in contrast, occurs nonlocally upon inelastic resonant scattering off single atomic defects at the edges. Our findings offer a crucial insight into the mechanisms that conceal the true topological protection and suggest venues for engineering more robust quantum states. 
Tuesday, March 3, 2020 1:03PM  1:39PM 
G37.00004: Nodal points of Weyl semimetals survive the presence of moderate disorder Invited Speaker: Michael Buchhold This talk addresses the physics of individual threedimensional Weyl nodes subject to a moderate concentration of disorder. Previous analysis indicates the presence of a quantum phase transition below which disorder becomes irrelevant and the integrity of sharp nodal points of vanishing spectral density is preserved in this system. This statement appears to be at variance with the inevitable presence of statistically rare fluctuations which cannot be considered as weak and must have strong influence on the system's spectrum, no matter how small the average concentration. We here reconcile the two pictures by demonstrating that rare fluctuation potentials in the Weyl system generate a peculiar type of resonances which carry spectral density in any neighborhood of zero energy, but never at zero. In this way, the vanishing of the DoS for weak disorder survives the inclusion of rare events. We demonstrate this feature by considering three different models of disorder, each emphasizing specific aspects of the problem: a simplistic box potential model, a model with Gaussian distributed disorder, and one with a finite number of s wave scatterers. 
Tuesday, March 3, 2020 1:39PM  2:15PM 
G37.00005: Spectrumwide quantum criticality at the surface of class AIII topological phases: An "energy stack" of integer quantum Hall plateau transitions Invited Speaker: Bjoern Sbierski In the absence of spinorbit coupling, the conventional dogma of Anderson localization asserts that all states localize in two dimensions, with a glaring exception: the quantum Hall plateau transition (QHPT). In that case, the localization length diverges and interferenceinduced quantumcritical spatial fluctuations appear at all length scales. Normally QHPT states occur only at isolated energies; accessing them therefore requires finetuning of the electron density or magnetic field. In this paper we show that QHPT states can be realized throughout an energy continuum, i.e. as an "energy stack" of critical states wherein each state in the stack exhibits QHPT phenomenology. The stacking occurs without finetuning at the surface of a class AIII topological phase, where it is protected by U(1) and (anomalous) chiral or timereversal symmetries. Spectrumwide criticality is diagnosed by comparing numerics to universal results for the longitudinal Landauer conductance and wave function multifractality at the QHPT. Results are obtained from an effective 2D surface field theory and from a bulk 3D lattice model. We demonstrate that the stacking of quantumcritical QHPT states is a robust phenomenon that occurs for AIII topological phases with both odd and even winding numbers. The latter conclusion may have important implications for the still poorlyunderstood logarithmic conformal field theory believed to describe the QHPT. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2024 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700