Estimation of Gr\"uneisen Parameter of Layered Superconductor LaO0.5F0.5BiS2-xSex (x = 0.2, 0.4, 0.6, 0.8, 1.0)

TL;DR

This study investigates how the Grüneisen parameter relates to superconductivity in LaO0.5F0.5BiS2-xSex, showing that increased lattice anharmonicity correlates with higher Tc and bulk superconductivity.

Contribution

It provides new insights into the relationship between lattice anharmonicity, as measured by the Grüneisen parameter, and superconducting properties in layered BiS2-based superconductors.

Findings

Higher Grüneisen parameter correlates with increased Tc.

Se substitution induces bulk superconductivity.

Presence of low-energy optical phonon mode suggested.

Abstract

The superconducting properties and structural parameters, including the Gr\"uneisen parameter ({\gamma}G), 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. {\gamma}G exhibited a larger value when x greater than 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 {\gamma}G 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.