Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B04: Driven Topological Quantum MaterialsInvited
|
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Jian-Xin Zhu, Los Alamos Natl Lab Room: LACC 151 |
Monday, March 5, 2018 11:15AM - 11:51AM |
B04.00001: Using Ultrashort Light Pulses to Probe and Control Quasiparticle Dynamics in Topological Materials Invited Speaker: Rohit Prasankumar Low energy excitations can shed light on the interplay between different degrees of freedom in complex materials. Ultrashort optical and terahertz (THz) pulses can be used to both drive and probe these excitations. This is particularly useful in topological materials, since coupling these excitations to light can potentially enable control of their properties. Here, the use of ultrafast THz spectroscopy to separately probe the dynamics of surface and bulk carriers and drive nonlinear phonon dynamics in the topological insulator Bi2Se3 will be discussed. We will also describe recent experiments using nonlinear optical techniques to examine quasiparticle dynamics in the Weyl semimetals WTe2 and TaAs. |
Monday, March 5, 2018 11:51AM - 12:27PM |
B04.00002: Light controlled topological phase transitions in multi-orbital and frustrated magnetic systems Invited Speaker: Thomas Devereaux Spurred by recent progress in melting, enhancement and induction of electronic order out of equilibrium, a tantalizing prospect concerns instead accessing transient Floquet steady states via broad pump pulses, to affect electronic properties. Here, we consider a two-pronged approach to manipulate the topology of a band insulator, as well as topological order in a Mott insulator. We first consider monolayer transition-metal dichalcogenides (TMDCs), and show that their low-energy description as massive 2D relativistic fermions fails to hold for optical pumping. Instead, the added complexity of a realistic materials description leads to a novel mechanism to optically induce topologically-protected chiral edge modes, facilitating optically-switchable conduction channels that are insensitive to disorder. We develop a strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions directly from ab initio calculations, and illustrate for the example of WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details. Second, we extend these ideas to strongly correlated systems and show that pumping frustrated Mott insulators with circularly-polarized light can drive the effective spin system across a phase transition to a chiral spin liquid (CSL). We show that the transient time evolution of a Kagome lattice Hubbard model is well captured by an effective spin description, where circular polarization promotes a staggered scalar spin chirality directly to the Hamiltonian level. We fingerprint the ensuing phase diagram and find a stable photo-induced CSL in proximity to the equilibrium ground state. The results presented suggest new avenues to marry dynamical symmetry breaking, strong interactions, and ab initio materials modelling, to access elusive phase transitions that are not readily accessible in equilibrium. |
Monday, March 5, 2018 12:27PM - 1:03PM |
B04.00003: Photoemission Studies of Topological Superconducting Materials Invited Speaker: Madhab Neupane A three-dimensional (3D) topological insulator (TI) is a crystalline solid, which is an insulator in the bulk but features spin-polarized Dirac electron states on its surface. In 2007, the first 3D TI was discovered in a bismuth-based compound. The discovery of the first TI tremendously accelerated research into phases of matter characterized by nontrivial topological invariants. Not only did the 3D TI itself attract great research interest, it also inspired the prediction of a range of new topological phases of matter. Primary examples include the topological Kondo insulator, the topological 3D Dirac, Weyl, and nodal-line semimetals, the topological crystalline insulator, and the topological superconductor. Specifically, recent predictions have claimed that long-sought-out Majorana fermions can be realized at the interface between a topological insulator and a superconductor and may shift our scientific trajectory from research to applications in topological quantum computing. In this talk, I will discuss the electronic properties of topological superconducting materials obtained by using momentum-, spin-, and time-resolved photoemission spectroscopy. Developing our understanding of topological superconducting materials will guide us on a path to realize the properties of Majorana fermion quasiparticle states associated with topological superconductivity. |
Monday, March 5, 2018 1:03PM - 1:39PM |
B04.00004: Spin-charge conversion in topological materials via THz emission spectroscopy Invited Speaker: Ee Min Chia In this talk I will show THz emission data from spin-to-charge conversion processes occuring in topological material (TM)/ferromagnet (FM) heterostructures, where the TM is the Bi2Se3 topological insulator or the MoS2 2D transition metal dichalcogenide, both of which possess large spin-orbit coupling. By measuring the emitted THz pulses in the time and frequency domain, as a function of pump polarization angle, pump fluence, magnetic field direction, sample direction, TM thickness, FM thickness and temperature, both in the pure TM film and the TM/FM heterostructure, we demonstrate highly-efficient THz emission from both Bi2Se3/Co and MoS2/Co. In Bi2Se3/Co, we conclude that the Bi2Se3 surface states play a dominant role in THz emission via the inverse Rashba-Edelstein effect. Compared to the instantaneous shift current THz emission mechanism in pure Bi2Se3, we observe a temporal delay in the spin-current-related component ~0.12 ps, which characterizes the spin-to-charge conversion timescale in topological insulators. In MoS2/Co, we observe and disentangle the contributions of inverse spin Hall effect and inverse Rashba-Edelstein effect to the spin-to-charge conversion. Our analysis gave estimates for the spin Hall angle, which is a measure of the spin-charge conversion efficiency, and the spin diffusion length, that enables us to resolve the spin diffusion dynamics from the Co layer into the TM surface. |
Monday, March 5, 2018 1:39PM - 2:15PM |
B04.00005: Topological frequency conversion in strongly driven quantum systems Invited Speaker: Gil Refael When a small quantum system is subject to multiple periodic drives, it may realize multidimensional topological phases. In my talk, I will explain how to make such constructions, and show how a spin-1/2 particle driven by two elliptically-polarized light beams could realize the Bernevig-Hughes-Zhang model of 2 topological insulators. The observable consequence of such a construction is quantized pumping of energy between the two drive sources. I will also show that the topological pumping quantization is not only robust against smooth temporal disorder, but even enforced by it. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit 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 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700