Identifying the Dirac point composition in Bi1−xSbx alloys using the temperature dependence of quantum oscillations

The thermal chiral anomaly is a new mechanism for thermal transport that occurs in Weyl semimetals (WSMs). It is attributed to the generation and annihilation of energy at Weyl points of opposite chirality. The effect was observed in the Bi1−xSbx alloy system, at x = 11% and 15%, which are topological insulators at zero field and driven into an ideal WSM phase by an external field. Given that the experimental uncertainty on x is of the order of 1%, any systematic study of the effect over a wider range of x requires precise knowledge of the transition composition xc at which the electronic bands at the L-point in these alloys have Dirac-like dispersions. At x > xc, the L-point bands are inverted and become topologically non-trivial. In the presence of a magnetic field along the trigonal direction, these alloys become WSMs. This paper describes how the temperature dependence of the frequency of the Shubnikov–de Haas oscillations F(x,T) at temperatures of the order of the cyclotron energy can be used to find xc and characterize the topology of the electronic Fermi surface. Semimetallic Bi1−xSbx alloys with topologically trivial bands have dF(x,T)/dT ≥ 0; those with Dirac/Weyl fermions display dF(x,T)/dT