Crystal Structure, Lattice Vibrations, and Superconductivity of LaO$_{1-x}$F$_{x}$BiS$_{2}$

TL;DR

This study investigates the crystal structure, lattice vibrations, and superconductivity in LaO$_{1-x}$F$_{x}$BiS$_{2}$, revealing how F-doping affects phonon modes and lattice parameters, and comparing experimental results with theoretical predictions.

Contribution

It provides detailed neutron scattering data and phonon mode analysis for LaO$_{1-x}$F$_{x}$BiS$_{2}$, combining experimental and theoretical approaches to understand its superconducting properties.

Findings

F-doping causes lattice contraction along c and slight expansion along a

High energy phonon modes change significantly with F substitution

Low energy phonon modes remain nearly unchanged across the superconducting transition

Abstract

Neutron scattering measurements have been performed on polycrystalline samples of the newly discovered layered superconductor LaO$_{0.5}$F$_{0.5}$BiS$_{2}$, and its nonsuperconducting parent compound LaOBiS$_{2}$. The crystal structures and vibrational modes have been examined. Upon F-doping, while the lattice contracts significantly along $c$ and expands slightly along $a$, the buckling of the BiS$_2$ plane remains almost the same. In the inelastic measurements, a large difference in the high energy phonon modes was observed upon F substitution. Alternatively, the low energy modes remain almost unchanged between non-superconducting and superconducting states either by F-doping or by cooling through the transition temperature. Using density functional perturbation theory we identify the phonon modes, and estimate the phonon density of states. We compare these calculations to the current measurements and other theoretical studies of this new superconducting material.