In-plane Charge Fluctuations in Bismuth Sulfide Superconductors

TL;DR

This paper presents evidence of local charge fluctuations and lattice distortions in LaO$_{1-x}$F$_{x}$ BiS$_{2}$ superconductors, suggesting a link between charge disproportionation, lattice distortions, and superconductivity.

Contribution

It provides experimental evidence of in-plane charge fluctuations and lattice distortions, proposing a mechanism involving charge density fluctuations and spin-orbit coupling for superconductivity.

Findings

Charge disproportionation of Bi ions observed.

In-plane sulfur atom distortions up to 0.3 Å detected.

Out-of-plane sulfur motion may facilitate charge transfer.

Abstract

Evidence for local charge fluctuations linked to a charge disproportionation of the Bi ions in the distorted lattice of superconducting LaO$_{1-x}$F$_{x}$ BiS$_{2}$ is presented. In-plane short-range distortions of sulfur atoms up to 0.3 \AA\ in magnitude break site symmetry and create two distinct environments around Bi. Out-of-plane motion of apical sulfur brings it closer to the La-O/F doping layer with increasing $x$ that may lead to a charge transfer conduit between the doping layers and the superconducting BiS$_{2}$ planes. The mechanism for superconductivity may arise from the interplay between charge density fluctuations and an enhanced spin-orbit coupling suggested theoretically, that induces spin polarization.