*

A significant enhancement of magneto thermal conductivity in semimetal Bi_1-x Sb_x alloy for a particular Sb concentration x=11% was discovered. As shown in a previous theoretical work on Weyl semimetals [1], Fermi arcs provide efficient ``conveyor belt'' for magneto thermal transport. In this talk, we argue that Bi_1-x Sb_x becomes a Weyl semimetal under magnetic field and the enhancement of magneto thermal conductivity is due to the resulting Fermi arcs, based on the tight binding parameterization calculated by a modified virtual crystal approximation. By calculating Chern numbers on two-dimensional slices of the three-dimensional Brillouin zone, we show that a pair of Weyl points appear near L points above a critical field strength, and that the seperation between those Weyl points increases with the field strength which explains the anomalous angular dependence of magneto thermal conductivity on magnetic field.

[1] T. McCormick et al., Phys. Rev. B 97 195152 (2018)