Role of local atomic displacements in the superconductivity of Sr_(0.5)La_(0.5)FBiS_2 and Sr_(0.5)La_(0.5)FBiSe_2 system

摘要

As new family of superconductors with layered structure, BiS2-based superconductors have attracted a large amount of attention. Recently, by the substitution of Se for S, isostructural BiSe2-based compounds have been reported to exhibit enhanced-superconductivity. In this contribution, we studied the local atomic displacements in Sr0.5La0.5FBiS2and Sr0.5La0.5FBiSe2samples by BiL3-edge extended X-ray absorption fine structure (EXAFS) to understand their correlation with the superconductivity. Compared to the case in Sr0.5La0.5FBiS2, the shortening of BiSe2 bond distance would strengthen the coupling between Sr/LaF layers and BiSe2layers, beneficial to the transfer of electrons into superconducting layers. On the other hand, the flatter BiSe1 plane in Sr0.5La0.5FBiSe2would 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 BiSe2-based system.