Lattice Anharmonicity in BiS2-Based Layered Superconductor RE(O,F)BiS2 (RE = La, Ce, Pr, Nd)

TL;DR

This study investigates how lattice anharmonicity, measured by the Grüneisen parameter, correlates with superconducting transition temperature in layered BiS2-based superconductors, revealing that increased anharmonicity enhances Tc.

Contribution

It demonstrates the positive correlation between lattice anharmonicity and Tc in REO1-xFxBiS2, highlighting the role of anharmonic vibrations in superconducting pairing mechanisms.

Findings

Higher {b3}G correlates with increased Tc.

In-plane chemical pressure increases bulk modulus and anharmonicity.

Reducing F concentration slightly decreases {b3}G.

Abstract

We studied Gr\"uneisen parameter ({\gamma}G) to investigate lattice anharmonicity in a layered BiS2-based superconductor system REO1-xFxBiS2 (RE = La, Ce, Pr, Nd), where in-plane chemical pressure was tuned by substituting the RE elements. With increasing in-plane chemical pressure, bulk modulus remarkably increases, and a high {\gamma}G is observed for RE = Nd. The dependence of {\gamma}G on in-plane chemical pressure exhibits a good correlation with Tc, and a higher Tc is achieved when {\gamma}G is large for RE = Nd. In addition, {\gamma}G shows a slight decrease by a decrease of F concentration (x) in REO1-xFxBiS2. Our results show that the anharmonic vibration of Bi along the c-axis is present in REO1-xFxBiS2, and the enhancement of the anharmonicity is positively linked to superconducting Tc and pairing mechanisms.