Electron Transfer and Local Atomic Displacement in Sr1-xCexFBiS2 Revealed by X-ray Absorption Spectroscopy

Superconductivity in quasi-two-dimensional crystal Structures has attracted sustained interest among condensed matter community, primarily due to their exotic superconducting properties. Recently, superconductivity of BiS2-based compounds with the desired layered crystal structure has been reported. In this contribution, Ce-doping effect on-the electronic structure and local atomic displacement of Sr1-xCexFBiS2 was investigated by Ce and Bi L-3-edge X-ray absorption spectroscopy. Upon Ce-doping both the Ce-S2 and Bi-S2 bonds shrink, enhancing the coupling between Sr/CeF and super-conducting BiS2 layers. Therefore, Ce substitution provides electron carriers to the superconducting BiS2 layers through the enhanced Ce-S2-Bi channel. On the other hand, Ce-doping effectively modulates the in-plane structure of Bi-S1 plane. In Ce-doped compounds both the shortening of in-plane Bi-S1 bond and the flatter Bi-S1 plane would enhance overlap of Bi(6p(x)/6p(y))-S(3p) orbitals within the superconducting plane. Therefore, Ce-doping not only provides the electron carriers to superconducting BiS2 layers, but also results in the flatter Bi-S1 plane. This may be related to the enhancement of superconductivity in Ce-doped SrFBiS2 compounds.