Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A45: Dirac and Weyl Semimetals: Optical and Transport PropertiesLive
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Sponsoring Units: DCMP Chair: Fernando De Juan, Donostia International Physics Center |
Monday, March 15, 2021 8:00AM - 8:12AM Live |
A45.00001: Chiral kinetic theory of anomalous transport induced by torsion GAO LANLAN, Sahal Kaushik, Dmitri E Kharzeev, Evan Philip In twisted Weyl semimetals, there are two different kinds of chirality: i) the (coordinate-space) |
Monday, March 15, 2021 8:12AM - 8:24AM Live |
A45.00002: Chiral electronics and effect of the external fields in topological semimetals Yuriko Baba, Álvaro Diaz, Enrique Benito-Matías, Gloria Platero, Elena Díaz, Francisco Domínguez-Adame, Rafael A. Molina Topological semimetals, such as Weyl and Dirac 3D semimetals, have attracted much interest in the last decade due to the promising new properties, especially related to their robust metallic surface states, called Fermi arcs. The effect of external perturbations such as electric fields or inversion-breaking terms enables the tuning of the surface states leading to non-trivial effects in transport properties. |
Monday, March 15, 2021 8:24AM - 8:36AM Live |
A45.00003: Optical signatures of multifold fermions in the chiral topological semimetals RhSi and CoSi Miguel Ángel Sánchez Martínez, Bing XU, Zhenyao Fang, Zhuoliang Ni, Jorn W. F. Venderbos, Fernando De Juan, Eugene John Mele, Andrew Marshall Rappe, Adolfo G Grushin, Liang Wu The chiral topological semimetals RhSi and CoSi exhibit band degeneracies near the Fermi level enforced by the crystal symmetries. The low-energy quasiparticles emerging near these band degeneracies, referred to as multifold fermions, have no counterpart as elementary fermionic particles. We calculate the linear optical conductivity of all chiral multifold fermions[1] and show that it provides an experimental fingerprint for each type of multifold fermion. We use a tight-binding model for space group 198, where RhSi and CoSi crystallize, and obtain the parameters for both materials from first-principles calculations. The results reveal that the location of the chemical potential is crucial to understand the optical response seen in experiments[2,3], determined at low energies by the threefold fermion at the Γ point in both materials, and providing signatures of the existence of a spin-3/2 fourfold fermion in CoSi. |
Monday, March 15, 2021 8:36AM - 8:48AM Live |
A45.00004: Chiral anomaly induced Veselago lensing in Weyl semimetals Serguei Tchoumakov, Bogusz Bujnowski, Jérôme Cayssol, Adolfo G Grushin The description of electron scattering between two media is similar to the refraction of light, where light-rays follow the path of least accumulated optical index. In the late 60's Veselago showed that this optical index can be negative, opening new ways for imaging, even below the diffraction limit. A similar situation also occurs in the case of Dirac electrons, in Klein tunneling. In this poster we show that on the contrary to 2D materials, such as graphene, Veselago lensing can be observed separately for cones of opposite chirality in Weyl semimetals with the help of the chiral anomaly. We illustrate this in the case of two physical phenomena : Friedel oscillations and non-local conductivity. This will allow us to discuss how Veselago lensing occurs in solid-state devices and its extensions to other types of materials. |
Monday, March 15, 2021 8:48AM - 9:00AM Live |
A45.00005: Ballistic feature in disordered Dirac and Weyl semimetals Koji Kobayashi, Miku Wada, Tomi Ohtsuki We study the dynamics of Dirac and Weyl electrons in disordered Dirac and Weyl semimetals. The ballistic feature of the transport is demonstrated by simulating the wave-packet dynamics on lattice models. We show that the ballistic transport survives under a considerable strength of disorder up to the semimetal-metal transition point, which indicates the robustness of Dirac and Weyl semimetals against disorder. We also visualize the robustness of the nodal points and linear dispersion under broken translational symmetry. In addition, scaling behavior of the speed of ballistic transport is confirmed, which provides us an alternative way to evaluate the critical exponent for semimetal-metal transition. |
Monday, March 15, 2021 9:00AM - 9:12AM Live |
A45.00006: Circular photogalvanic effect in interacting Weyl semimetals Aleksandr Avdoshkin, Vladyslav Kozii, Joel Ellis Moore
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Monday, March 15, 2021 9:12AM - 9:24AM Live |
A45.00007: Anomalous transfer of chirality from light to fermions in Dirac and Weyl semimetals Evan Philip, Sahal Kaushik, Dmitri E Kharzeev Circularly polarized light possesses a non-zero chirality since it breaks the symmetry between left and right. When circularly polarized light interacts with Dirac and Weyl semimetals, we predict that chirality will be transferred from the electromagnetic field to the chiral quasiparticles in the semimetal. We show that if the photoresponse of the material is dominated by chiral quasiparticles, the total chiral charge induced in the material by light can be evaluated in a model-independent way through the chiral anomaly. In the presence of an external magnetic field, this would result in a photocurrent due to the chiral magnetic effect. The predicted photocurrent should manifest in any kind of Dirac or Weyl semimetal, with both symmetric and asymmetric band structure. This current scales linearly with the magnetic field and wavelength, opening up the possibility for a wide range of applications. |
Monday, March 15, 2021 9:24AM - 9:36AM Live |
A45.00008: Intrinsically Damped Optical Absorption in Dirac Metals Adamya Goyal, Abhishek Kumar, Dmitrii Maslov In an ideal Dirac metal, optical absorption is absent for frequencies below the Pauli threshold (twice the Fermi energy). In real systems, however, e.g., in doped graphene, both optical absorption [1] and Raman scattering [2] find a very broad transition region around the Pauli threshold. While a number of extrinsic damping mechanisms were proposed to explain this observation in the past, we argue that the effect can be explained by an intrinsic mechanism -- Auger-like recombination of optically excited minority carriers with equilibrium majority carriers. The idea goes back to a similar mechanism proposed for doped gapped semiconductors by Gavoret et al [3]. The width of the transition region in this mechanism is comparable to the Fermi energy. We also discuss a scenario in which the Auger width is small and thus well-defined excitons below the Pauli threshold become possible. |
Monday, March 15, 2021 9:36AM - 9:48AM Live |
A45.00009: Longitudinal magnetoconductance and the planar Hall effect in a lattice model of tilted Weyl fermions Azaz Ahmad, Girish Sharma The experimental verification of chiral anomaly in Weyl semimetals is an active area of investigation in modern condensed matter physics, which typically relies on the combined signatures of longitudinal magnetoconductance (LMC) along with the planar Hall effect (PHE). It has recently been shown that for weak non-quantizing magnetic fields, a sufficiently strong finite intervalley scattering drives the system to switch the sign of LMC from positive to negative. Here we unravel another independent source that produces the same effect. Specifically, a smooth lattice cutoff to the linear dispersion, which is ubiquitous in real Weyl materials, introduces nonlinearity in the problem and also drives the system to exhibit negative LMC for non-collinear electric and magnetic fields even in the limit of vanishing intervalley scattering. We examine longitudinal magnetoconductivity and the planar Hall effect semi-analytically for a lattice model of tilted Weyl fermions within the Boltzmann approximation. We independently study the effects of a finite lattice cutoff and tilt parameters and construct phase diagrams in relevant parameter spaces that are relevant for diagnosing chiral anomaly in real Weyl materials. |
Monday, March 15, 2021 9:48AM - 10:00AM Live |
A45.00010: Controlling symmetry and topology via bicircular light: application to Cd3As2 Thais Victa Trevisan, Pablo Villar Arribi, Olle Heinonen, Robert-Jan Slager, Peter Orth Light-matter interaction is a powerful tool to manipulate electronic properties of materials. Of particular interest are intense periodic light fields, which can be carefully tailored to dynamically manipulate materials’ properties via control of symmetry and band topology. A particularly versatile and less explored way of such Floquet engineering is to use a bicircular light, which is a superposition of two circularly polarized lights of different frequencies that are integer multiples of each other. In bicircular light, the electric field traces out a Lissajous figure in real space, which opens the intriguing possibility to precisely control spatial and magnetic symmetries, in addition to time-reversal symmetry. We apply bicircular light tuning to the Dirac semimetal Cd3As2 and demonstrate that the material can be driven into different Weyl semimetal phases, with interesting consequences on the protected surface states. |
Monday, March 15, 2021 10:00AM - 10:12AM Live |
A45.00011: Non-local optical plasmon supported by Fermi arc states in thin film Weyl semimetal Debasmita Giri, Dibya Kanti Mukherjee, Sonu Verma, Herb Fertig, Arijit Kundu The Fermi surface of a thin-film Weyl semimetal consists of highly anisotropic contours, each of which contains topologically protected Fermi arc states on the thin-film surfaces, as well as states with dominant support in the bulk of the system. We study collective charge oscillations for this system, uncovering a single optical plasmonic mode originating from collective oscillations on the two surfaces. Remarkably, these lowest frequency modes involve surface charges which oscillate out-of-phase, suggesting the resulting electric fields are relatively confined to the interior of the thin film. We discuss possible implications of our findings for plasmonic applications. |
Monday, March 15, 2021 10:12AM - 10:24AM Live |
A45.00012: Chiral-Anomaly-Induced Nonlinear Hall Effect in Tilted Weyl Semimetals Ruihao Li, Shulei Zhang, Olle Heinonen, Anton Burkov Weyl semimetals (WSMs) are a new class of quantum materials that can host massless quasiparticles called Weyl fermions. One unique feature of WSMs is the chiral anomaly – a pair of Weyl nodes of opposite chiralities acts as source and drain of electrons in the presence of parallel electric and magnetic fields. Hence, a steady-state density difference between a pair of Weyl nodes is established when the chiral pumping and the internode relaxation reach a balance, which conspires with the anomalous velocity of the electrons to give rise to a nonlinear Hall effect. In this work, we find that the chiral-anomaly-induced nonlinear Hall (CNH) effect requires inversion symmetry breaking as well as asymmetric Fermi surfaces, which may be realized in tilted WSMs wherein the overall tilting of the Weyl cones is asymmetric about the Γ point. We also show that this effect is different from the Berry-curvature-induced nonlinear Hall effect that exist in time-reversal invariant materials. We will also discuss the CNH effect in recently discovered magnetic noncentrosymmetric WSMs. |
Monday, March 15, 2021 10:24AM - 10:36AM Live |
A45.00013: Quantized Hall conductance in 3D topological nodal-line semimetals without chiral symmetry Guang-Qi Zhao, W. B. Rui, Chunming Wang, Haizhou Lu, X. C. Xie A quantized Hall conductance (not conductivity) in three dimensions has been searched for more than 30 years. Here we explore it in 3D topological nodal-line semimetals, by using a model capable of describing all essential physics of a semimetal, in particular the drumhead surface states protected by a momentum-dependent winding number. We develop a microscopic theory to demonstrate that the drumhead surface states can host quantized Hall conductance in this 3D material. We stress that breaking chiral symmetry is necessary for the quantum Hall effect of the drumhead surface states. The analytic theory can be verified numerically by the Kubo formula. There may also be trivial quantum Hall effects from the bulk states. We propose an experimental setup to distinguish the surface and bulk quantum Hall effects. The theory will be useful for ongoing explorations on nodal-line semimetals. |
Monday, March 15, 2021 10:36AM - 10:48AM Live |
A45.00014: Optical conductivity of Dirac Fermi liquid Prachi Sharma, Dmitrii Maslov A Dirac-Fermi liquid (DFL) —a doped system with Dirac spectrum—is a special and important subclass of non-Galilean-invariant Fermi liquids (FLs) which includes, e.g., graphene and the surface state of a three-dimensional topological insulator. We study the effect of electron-electron (ee) interactions on the optical conductivity of a DFL. We find that the effective current relaxation rate behaves as 1/τJ∼( 3ω4+20π2T2ω2+32 π4T4)/μ3 for max{ω, T}«μ, where μ is the chemical potential. The quartic term in 1/τJ competes with a small FL-like term, (ω2+4π2T2)/ μ, due to weak trigonal warping of graphene dispersion. In the presence of weak disorder, the optical conductivity is described by the sum of two Drude-like terms, with widths given by the ee and electron-impurity scattering rates, respectively. The dc resistivity varies non-monotonically with T, approaching the identical values given by the residual resistivity in the limits of both low and high T, with a maximum in between. We also calculated the dynamic charge susceptibility χc(q,ω) outside p-h continua to one-loop order in the dynamically screened Coulomb interaction. For a DFL, the dissipative part of χc(q,ω) scales as q2ω and is larger than the q4/ω scaling for a Galilean-invariant FL. |
Monday, March 15, 2021 10:48AM - 11:00AM On Demand |
A45.00015: Pseudo field effects in type II Weyl semimetals: new probes for over tilted cones Daniel Sabsovich, Tobias P Meng, Dmitry I. Pikulin, Raquel Queiroz, Roni Ilan We propose a probe for type II Weyl semimetals which determines the direction of the tilt. Building on the different phenomenology of the chiral Landau and pseudo-Landau levels in Weyl semimetals, we show how in a simple two Weyl cone model, the optical conductivity can be utilized to differentiate between the type I and II semimetals and pinpoint the direction of the tilt, and the field itself. For a larger number of nodes, a combination of the two fields can hint on the arrangement of cones as well. |
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