Evolution of Anisotropic Displacement Parameters and Superconductivity with Chemical Pressure in BiS2-Based REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd)

TL;DR

This study investigates how chemical pressure affects the crystal structure, anisotropic displacement parameters, and superconductivity in REO0.5F0.5BiS2 compounds, revealing a universal link between reduced in-plane disorder and superconductivity emergence.

Contribution

It provides new insights into the relationship between chemical pressure, structural disorder, and superconductivity in BiCh2-based materials, highlighting the universal role of in-plane disorder suppression.

Findings

In-plane disorder decreases with smaller RE ionic radius.

Suppression of in-plane disorder correlates with the emergence of superconductivity.

Vibration amplitude along the c-axis may influence Tc.

Abstract

In order to understand the mechanisms behind the emergence of superconductivity by the chemical pressure effect in REO0.5F0.5BiS2 (RE = La, Ce, Pr, and Nd), where bulk superconductivity is induced by the substitutions with a smaller-radius RE, we performed synchrotron powder X-ray diffraction, and analyzed the crystal structure and anisotropic displacement parameters. With the decrease of the RE3+ ionic radius, the in-plane disorder of the S1 sites significantly decreased, very similar to the trend observed in the Se-substituted systems: LaO0.5F0.5BiS2-xSex and Eu0.5La0.5FBiS2-xSex. Therefore, the emergence of bulk superconductivity upon the suppression of the in-plane disorder at the chalcogen sites is a universal scenario for the BiCh2-based superconductors. In addition, we indicated that the amplitude of vibration along the c-axis of the in-plane chalcogen sites may be related to the Tc in the BiCh2-based superconductors.