Large and Optimized Thermal Chiral Anomaly in Weyl Semimetal Bi-Sb

Abstract

Weyl semimetals are bulk solids in which chiral anomalies, i.e., negative magnetoelectric and magnetothermal resistances, exist as a result of the chiral properties of the Weyl fermions. The thermal chiral anomaly has potential in devices that actively control heat fluxes; these would be an early application of topological properties, realized after the materials are optimized. Here, we optimized the band structure of Bi1-xSbx alloys in the topological insulator phase and in their field-induced Weyl semimetal phases to maximize the thermal chiral anomaly by changing the Sb concentration and by doping Bi1-xSbx alloys either with n-type Te or with p-type Sn. We show that the chiral anomalies are maximized when the chemical potential is at the Weyl points and that Weyl fermions are protected against scattering on phonons and neutral defects but not necessarily on charged particles like ionized impurities and electrons in trivial pockets. In our optimum material, around 30% of the total heat (carried by phonons, trivial electrons, and the chiral anomaly) is carried by the anomalous heat current (the chiral anomaly). The latter is highly switchable under a magnetic field. The maximum effect we observe is an anomalous thermal conductivity at 7 T that is 700% larger than the zero-field electronic thermal conductivity at T= 40 K in a x = 0.1 sample with p-type doping to 3.90 x 10(15) cm(-3) with a mobility of 2 350 000 cm(2) V-1 s(-1).