Role of local atomic displacements in the superconductivity of Sr0.5La0.5FBiS2 and Sr0.5La0.5FBiSe2 system

Abstract As new family of superconductors with layered structure, BiS 2 -based superconductors have attracted a large amount of attention. Recently, by the substitution of Se for S, isostructural BiSe 2 -based compounds have been reported to exhibit enhanced-superconductivity. In this contribution, we studied the local atomic displacements in Sr 0.5 La 0.5 FBiS 2 and Sr 0.5 La 0.5 FBiSe 2 samples by Bi L 3 -edge extended X-ray absorption fine structure (EXAFS) to understand their correlation with the superconductivity. Compared to the case in Sr 0.5 La 0.5 FBiS 2 , the shortening of Bi Se2 bond distance would strengthen the coupling between Sr/LaF layers and BiSe 2 layers, beneficial to the transfer of electrons into superconducting layers. On the other hand, the flatter Bi Se1 plane in Sr 0.5 La 0.5 FBiSe 2 would enhance the orbital overlap within the superconducting plane. Consequently, an enhanced interlay coupling and a flatter superconducting plane may be related to the enhancement of superconductivity in BiSe 2 -based system.