Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z44: Anomalies in Topological Weyl SemimetalsInvited Live Streamed

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Sponsoring Units: DCMP GMAG Chair: Jukka Vayrynen, Purdue University Room: McCormick Place W375C 
Friday, March 18, 2022 11:30AM  12:06PM 
Z44.00001: Thermal chiral anomaly in the magneticfield induced ideal Weyl phase of Bi1xSbx topological insulators Invited Speaker: Joseph P C Heremans Bi(1x)Sb(x) alloys with x>9% are topological insulators. In a quantizing magnetic field applied along the trigonal direction, their bandgap decreases with field because the Zeeman energy exceeds the orbital Landau level energies. They turn into fieldinduced Weyl semimetals, with 6 pairs of 2 degenerate Weyl points centered around the Lpoints of the Brillouin zone. The Weyl point separation is mosty parallel to the applied field. It scales with magnetic field intensity. Because Bi and Sb are isoelectronic, the sample's unintentional doping levels can be kept minimum. Large single crystals with residual carrier concentrations in the 1E15 cm^3 range and mobilities of the order of several million cm^2/V.s at 10K have been grown that have the chemical potential within a few meV of the Weyl point energy and reach the extreme quantum limit at 13 Tesla depending on x. This talk will review the thermal, thermoelectric and electrical properties of these ideal Weyl semimetals. The chiral anomaly is the dominant feature of the magnetoresistance, after care has been taken to avoid current jetting and geometrical magnetoresistane effects. The thermal chiarl anomaly (gravitational anomaly) increases the electronic thermal conductivity (x  11%) by 300 % in a field of 9T, becoming also the dominant feature of the thermal conductivity The thermal effect are observed from 35 K (below which the lattice thermal conductivity dominates) to 200 K, almost twice the Debye temperature, which shows that the effect is robust to phonon scattering. It is observed in samples with mobilities as low as 50,000 cm^2/V.s at 10K, indicating robustness to defect scattering. The talk will further review the dependence of the effect to Sb concentration in the range 4% 
Friday, March 18, 2022 12:06PM  12:42PM 
Z44.00002: Thermal transport and gravitational anomalies in Weyl semimetals. Invited Speaker: Adolfo G Grushin A handfull of recent thermal transport experiments have been interpreted as a measurement of an elusive gravitational anomaly, an exotic quantum mechanical phenomenon that is associated to strong gravitational fields, like those near blackholes. They raise the challenge to find a clear link between gravitational anomalies, that require strong gravitational fields, and condensed matter experiments, that are realized in negligable gravitational fields. Finding this link requires to go beyond a commonplace idea due to Luttinger, who noticed that thermal transport caused by a thermal gradient is analogous to transport caused by an auxiliary gravitational field. The reason is that Luttinger developed this "trick" for small gravitational fields, far from those that activate the anomaly. The failure of Luttinger idea is the open problem that I will address in my talk. I will review the different links between thermal transport and gravitational anomalies that have been suggested. I will end by discussing our own ongoing efforts to understand how Luttinger's trick can succeed in strong gravitational fields. 
Friday, March 18, 2022 12:42PM  1:18PM 
Z44.00003: Fundamental relations for anomalous thermoelectric transport coefficients for Weyl semimetals in the nonlinear regime Invited Speaker: Sumanta Tewari Anomalous Hall and Nernst effects in timereversalsymmetric systems have recently been theoretically discussed in the nonlinear regime and have seen some early success in 
Friday, March 18, 2022 1:18PM  1:54PM 
Z44.00004: Quantum anomalies and quantum geometry induced linear and nonlinear transport in Weyl semimetals Invited Speaker: Amit Agarwal Quantum geometry of the electron wavefunction plays a significant role in the linear and nonlinear responses of Weyl semimetals. One such geometric quantity, the Berry curvature can be used to understand the quantum anomalies in Weyl semimetal, which leads to chiral charge and energy pumping between the Weyl nodes of opposite chirality. This results in chiral charge and energy imbalance between the Weyl nodes and gives rise to several intriguing magnetotransport phenomena. In addition to the Berry curvature, other band geometric quantities such as the orbital magnetic moment, Berry curvature dipole, and the quantum metric also give rise to novel transport phenomena in Weyl semimetals. 
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