Improvement of superconducting properties by high mixing entropy at blocking layers in BiS2-based superconductor REO0.5F0.5BiS2

TL;DR

This study demonstrates that increasing mixing entropy in the blocking layers of BiS2-based superconductors enhances bulk superconductivity by reducing in-plane disorder, revealing a new way to improve superconducting properties.

Contribution

It provides the first systematic investigation of how high mixing entropy in blocking layers influences superconductivity in REO0.5F0.5BiS2 compounds.

Findings

Higher mixing entropy suppresses in-plane S1 site disorder.

Bulk superconductivity is enhanced with increased DSmix.

Increase in DSmix does not significantly alter bond lengths or angles.

Abstract

To investigate the interlayer interaction in the recently synthesized high-entropy-alloy-type (HEA-type) REO0.5F0.5BiS2 superconductors (RE: rare earth), we have systematically synthesized samples with close lattice parameters and different mixing entropy (DSmix) for the RE site. The crystal structure was investigated using synchrotron X-ray diffraction and Rietveld refinement. For the examined samples with different DSmix, the increase in DSmix does not largely affect the bond lengths and the bond angle of the BiS2 conducting layer but clearly suppresses the in-plane disorder at the in-plane S1 site, which is the parameter essential for the emergence of bulk superconductivity in the REO0.5F0.5BiS2 system. Bulk nature of superconductivity is enhanced by the increase in DSmix for the present samples. The results of this work clearly show that the increase in mixing entropy at the blocking layer can positively affect the emergence of bulk superconductivity in the conducting layer, which is the evidence of the interaction between the high entropy states of the blocking layers and the physical properties of the conducting layers.