Estimation of Grüneisen Parameter of Layered Superconductor LaO0.5F0.5BiS2−xSex (\(x = 0.2,0.4,0.6,0.8,1.0\))

The superconducting properties and structural parameters, including the Grüneisen parameter (γG), of the BiCh2-based (Ch: S, Se) layered superconductor LaO0.5F0.5BiS2−xSex were investigated. The superconducting transition temperature (Tc) increased with increasing Se concentration (x), and bulk superconductivity was induced by Se substitution. γG exhibited a larger value when x ≥ 0.4, where the superconducting properties were improved. These results suggest that the increase of lattice anharmonicity is preferable for superconductivity in LaO0.5F0.5BiS2−xSex. The discussion includes data for related superconductors REO0.5F0.5BiS2 (RE = Pr, Nd), where a positive correlation between γG and Tc is revealed for Se-poor samples. In addition, specific heat analyses suggest the presence of a low-energy optical phonon mode for LaO0.5F0.5BiS2−xSex.