Emerging Superconductivity and Topological States in Bismuth Chalcogenides

Abstract

In this chapter, we review the recent experimental work in emerging superconductors, i.e., bismuth chalcogenides, including the newly discovered BiS(e) 2 -based layered superconductors and some topological superconductor candidates. Their crystal structure and various physical properties are reviewed in detail, with the correlation between structure and superconductivity as the main clue throughout this chapter. Bi 2 OS 2 is the sim- plest structure in Bi ─ O ─ S compounds and probably the parent compound of this series. Superconductivity emerges when carriers are introduced by intercalation or chemical substitution. The superconducting layer is extended to BiSe 2 layer in LaO 1−x F x BiSe 2 , which has an improved superconductivity. Moreover, the topological insulator Bi 2 Se 3 can be turned into superconductors by intercalating metal atoms into van der Waals space, e.g., Sr x Bi 2 Se 3 , a potential topological superconductor, whose quantum oscillations reveal a possible topological surface state. The intermediate external pressure can efficiently sup press superconductivity, which reemerges when pressure is further increased, while T c is nearly invariant in high-pressure region, indicating an unconventional pairing state.