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 R50: Interplay of Electronic Topology with Magnetic, Superconducting, and Crystalline OrdersInvited Live
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Sponsoring Units: DCMP Chair: Alexis Chacon, Max Planck POSTECH KRI |
Thursday, March 18, 2021 8:00AM - 8:36AM Live |
R50.00001: Magnetic Weyl semimetals and nodal line materials Invited Speaker: Claudia Felser Recently the combination of magnetism and topology is a new exciting direction in condensed matter physics [1,2]. In magnetic materials the Berry curvature and the classical AHE helps to identify interesting candidates. Magnetic ferromagnetic Heusler compounds were predicted and already identified as Weyl semimetals and nodal line materials such as Co2YZ [3-6] (Y=Ti, Mn; Z=Ge, Sn, Ga, Al). Kagome lattice compounds are another tunable class and ferromagnetic Co3Sn2S2 is a more 2D Weyl semimetal [7-9]. Beside the smoking gun experiments: Fermi arc and chiral anomaly [6,8,9] all these materials show giant responses: an anomalous Hall and an anomalous Nernst effect [10-13]. Beloposki et al. observed nodal lines and the related drum head surface states in Co2MnGa via angle-resolved photoemission spectroscopy [5]. In Co2MnAl a large AHE was already observed in 2011, with an application for anomalous Hall effect sensors in mind . The anomalous Hall effect in Co2MnGa and Co2MnAl is large, leading to a Hall angle of 12% and 21 %, respectively [11,13]. |
Thursday, March 18, 2021 8:36AM - 9:12AM Live |
R50.00002: Multiple topological facets of Bismuth Invited Speaker: Nurit Avraham Bismuth, due to its large spin-orbit coupling, plays a fundamental role in many topological materials. Yet the topological classification of pure Bismuth has remained, thus far, rather ambiguous. While some theoretical models indicate its trivial topological nature, other theoretical and experimental studies suggest non-trivial topological classifications, such as a strong or a higher order topological insulator. I will explain the origin for this ambiguity and present scanning tunneling microscopy data in which we resolve the topological classification of Bismuth, as a strong topological insulator with weak indices, by spectroscopically mapping the response of its boundary modes to a topological defect in the form of a screw dislocation [1]. Next, I will present our work on Bi2TeI, which consists of a stack of Bi-bilayers. Our data shows that in this form the topological nature is of a dual topological insulator [2]. Bi2TeI hosts a weak topological insulator surface state on its ‘side’ facets and a topological crystalline insulator surface state protected by mirror symmetry on its top and bottom facets. We visualize the topological crystalline surface states and show their sensitivity to mirror symmetry-breaking as well as the one dimensional channels, derived from the 2D weak topological insulator states, which run along step-edges. We studied the coexistence of the two types of states on step-edges, where both facets join. Our measurements reveal that the two types of states remain well decoupled from one another due to separation in momentum space and in energy. We show, however, that this protection is susceptible to strong disorder. |
Thursday, March 18, 2021 9:12AM - 9:48AM Live |
R50.00003: Chern numbers and nodal points in topological semi metals. Invited Speaker: Maia Garcia Vergniory Nonmagnetic topological materials have dominated the landscape of topological physics for the past two decades. These breakthroughs in non-magnetic materials have not yet been matched by similar advances in magnetic compounds. Using magnetic band theory and topological indices obtained from Magnetic Topological Quantum Chemistry (MTQC), I will present a systematic way of identifying magnetic topological materials. I will then, focus on high order magnetic semimetals, and provide a topological classification of different fermions in these phases. Finally I will present new experimental realizations in materials. In particular I will focus on the pyrite compound CoS2, using complementary bulk- and surface-sensitive angle-resolved photoelectron spectroscopy and ab-initio calculations we discovered Weyl-cones at the Fermi-level and we directly observed the topological Fermi-arc surface states that link the Weyl-nodes, which will influence the performance of CoS2 as a spin-injector by modifying its spin-polarization at interfaces. |
Thursday, March 18, 2021 9:48AM - 10:24AM Live |
R50.00004: Chiral topological superconductivity in the heavy fermion superconductor UTe2 Invited Speaker: Vidya Madhavan Topological superconductors represent a fundamentally new phase of matter. Similar to topological insulators, the non-trivial topological characteristics of a topological superconductor dictate the presence of a topological edge states composed of Bogoliubov quasiparticles which live inside and span the superconducting gap. The intense interest in these materials stems from the fact that Bogoliubov excitations inside the gap of a topological superconductor are predicted to have all the characteristics of Majorana Fermions. A chiral p-wave superconductor which is topologically non-trivial is a natural platform for realizing these Majorana modes. In this talk I present scanning tunneling microscopy (STM) data on the newly discovered heavy fermion superconductor, UTe2 with a TC of 1.6K. I will show signatures of coexisting Kondo effect and superconductivity which show competing spatial modulations within one unit-cell. STM spectroscopy at step edges show signatures of chiral in-gap states, predicted to exist at the boundaries of a topological superconductor. Combined with existing data indicating triplet pairing, the presence of chiral edge states suggests that UTe2 is a strong candidate material for chiral-triplet topological superconductivity. |
Thursday, March 18, 2021 10:24AM - 11:00AM Live |
R50.00005: Emergent pseudo-electromagnetic fields in topological semimetals Invited Speaker: Roni Ilan Spatial variations of strain or magnetization can create emergent intrinsic electromagnetic fields in topological semimetals. Such pseudo-electromagnetic fields are, however, different from external electromagnetic fields in their symmetries and phenomenology. We review the different mechanisms for creating effective pseudo-fields and their observable consequences, ranging from anomalous transport to sound absorption. |
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