  Superconductivity within layered crystal structures has attracted sustained
interest among condensed matter community, primarily due to their exotic
superconducting properties. EuBiS2F is a newly discovered member in the
BiS2-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 Tc enhancement have not yet been elucidated. In this study,
the Ce-doping effect on the self-electron-doped superconductor EuBiS2F was
investigated by X-ray absorption spectroscopy (XAS). We have established a
relationship between Ce-doping and the Tc 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 BiS2-based
superconductors.
