Interfacial thermal resistance associated with topologically protected interface states in topological phase

Below about 100 K, Bi_1-xSb_x alloys with 9 < x < 15% are topological insulators (TI)¹ that display clear surface states identified by ARPES, due to inverted band ordering of L bands. They are trivial semimetals for x < 5% or x > 20 %, topological semimetals for 5 < x < 9%, and indirect-gap semiconductors for 15 < x < 20%. Bi₈₉Sb₁₁ and Bi₈₇Sb₁₃ alloys undergo a topological phase transition from TI at low temperature to trivial semimetal as temperature rises because the band gap open with the change of lattice constant.^2,3 We use the temperature-induced TI/trivial semimetal phase transition in Bi₈₉Sb₁₁ and Bi₈₇Sb₁₃ to show the impact of the interface states on the interfacial thermal conductance. Using frequency-domain thermoreflectance (FDTR), we discover abrupt changes in interfacial thermal conductance of Au/Ti/Bi_1-xSb_x (x = 0.03, 0.11 and 0.13) system at the transition points, which we ascribe to the presence of topological interfacial states near the Fermi level. We then inject an electrical current in these interfaces and observe a strongly non-monotonic dependence of the interfacial thermal conductance on the applied bias voltage, which we attribute to tuning the Fermi energy away from Dirac points. This discovery might lead to the development of a proof-of-concept for all-solid-state thermal switches and regulators.



(1) Hsieh, D.; Qian, D.; Wray, L.; Xia, Y.; Hor, Y. S.; Cava, R. J.; Hasan, M. Z. A topological Dirac insulator in a quantum spin Hall phase. Nature 2008, 452, 970-974. https://doi.org/10.1038/nature06843.

(2) Cucka, P.; Barrett, C. S. The crystal structure of Bi and of solid solutions of Pb, Sn, Sb and Te in Bi. Acta Cryst. 1962, 15, 865. https://doi.org/10.1107/S0365110X62002297.

(3) Vandaele, K.; Otsuka, M.; Hasegawa, Y.; Heremans, J. P. Confinement effects, surface effects, and transport in Bi and Bi_1-xSb_x semiconducting and semimetallic nanowires. J. Phys.: Condens. Matter 2018, 30, 403001. https://doi.org/10.1088/1361-648X/aada9b.