Role of valence changes and nanoscale atomic displacements in BiS(2)-based superconductors

Superconductivity within layered crystal structures has attracted sustained interest among condensed matter community, primarily due to their exotic superconducting properties. EuBiS(2)F is a newly discovered member in the BiS(2)-based superconducting family, which shows superconductivity at 0.3 K without extrinsic doping. With 50 at.% Ce substitution for Eu, superconductivity is enhanced with Tc increased up to 2.2 K. However, the mechanisms for the T(c) enhancement have not yet been elucidated. In this study, the Ce-doping effect on the self-electron-doped superconductor EuBiS(2)F was investigated by X-ray absorption spectroscopy (XAS). We have established a relationship between Ce-doping and the T(c) enhancement in terms of Eu valence changes and nanoscale atomic displacements. The new finding sheds light on the interplay among superconductivity, charge and local structure in BiS(2)-based superconductors.