Interfacial thermal resistance in topological phases*

Bi_1-xSb_x alloys have various band structures depending on the Sb concentration.¹ In particular, when x is above 10%, the Bi_1-xSb_x alloys can be in topological insulator (TI) phase with the inverted band ordering of L bands, and the band gap can get reopened as temperature rises because lattice constant changes.^2,3 In this work, we use the band gap opening of TI Bi_1-xSb_x alloys with the increase of temperature and the accompanying phase transition from topological insulator into trivial semiconductor to study the thermal properties of the topological interface states near the Fermi level. By measuring the frequency-domain thermoreflectance (FDTR) data on Au/Bi_0.93Sb_0.07, Bi_0.9Sb_0.1 and Bi_0.87Sb_0.13­, we discover an abrupt change in interfacial thermal conductance of Au/Bi_1-xSb_x system that occurs at the TI/trivial transition point.  We attribute it to the change of thermal transport of electrons at the surface of Bi_1-xSb_x. This discovery might lead to the development of a proof-of-concept for all-solid-state thermal switches and regulators.