Superconductivity in semimetallic Bi₃O₂S₃

Here we report a further investigation on the thermodynamic and transport properties, and an assessment of theoretical calculations, for the BiS₂-layered Bi₃O₂S₃ superconductor. The polycrystalline sample is synthesized with a superconducting transition temperature of Tconset=5.75K and Tczero=4.03K (≈Tcmag) that drops to 3.3 K by applying a hydrostatic pressure of 6 kbar. Density-of-states (DOS) calculations give substantial hybridization between Bi, O, and S, with Bi the largest component of DOS, which supports the idea that the BiS2 layer is relevant for producing electron-phonon coupling. An analysis of previously published specific heat data for Bi₃O₂S₃ is additionally suggestive of a strong electron-phonon interaction in the Bi-O-S system. The analysis of the Seebeck coefficient results strongly suggests that Bi₃O₂S₃ is a semimetal. In fact, the semimetallic or narrow band gap behavior may occur in certain other materials in the BiS₂-layered class of materials, such as Bi₄O₄S₃.