On-line SPICE-SPIN+X Seminars
On-line Seminar: 27.01.2021 - 15:00 German Time
The Thermal Chiral Anomaly in ideal field-induced Weyl semimetals
Joseph Heremans, Ohio State University
The Thermal Chiral Anomaly in ideal field-induced Weyl semimetals.
Weyl semimetals (WSMs) are solids with a bulk band structure consisting of pairs of chirally distinct linear Dirac bands that intersect at the Weyl points. In ideal Weyl semimetals, where the electrochemical potential is located at the energy of the Weyl points, the Fermi surface in the bulk amounts to a pair of Weyl points of opposite chirality. Transport in ultra-quantum magnetic fields in an ideal WSM is subject to the chiral anomaly, an additional electrical conductivity that results from the generation of carriers of one chirality and the annihilation of carriers of the other in a magnetic field oriented parallel to the direction of the charge flux. In contrast the chiral anomaly in the electrical conductivity, there is no creation/annihilation of charge in the thermal conductivity, but there is an equivalent effect in the energy at both points, giving an excess thermal conductivity that we put in evidence experimentally. The thermal and electrical anomalies relate to each other by the Wiedemann-Franz law.
The experimental observations are made on the field-induced WSM Bi1-x¬Sbx (8 at%<x 1-to-4 T), transforming the semiconductor into a WSM. The samples display freeze-out upon cooling and show no Shubnikov–de Haas oscillations despite their high mobility (1.9 × 106 cm2V-1s-1 at 10 K), ensuring that the electrochemical potential is at the Weyl points. By construction, no trivial pockets exist in the Fermi surface, making this an ideal WSM. We observe an increase in thermal conductivity zz in longitudinal field Bz that is consistent with the theory and obeys the Wiedemann-Franz law wit the free electron value of the Lorenz ratio.
If time permits, preliminary data on the thermal Hall effect in the same samples will be presented. The thermal Hall effect behaves qualitatively differently from the electrical Hall effect, and may contain contributions from charge carriers on the Fermi arcs.