Density-functional calculations of the electronic structure and lattice dynamics of superconducting LaO$_{0.5}$F$_{0.5}$BiS$_{2}$: Evidence for an electron-phonon interaction near the charge-density-wave instability

TL;DR

This study uses density functional calculations to analyze the electronic structure and lattice dynamics of LaO$_{0.5}$F$_{0.5}$BiS$_{2}$, revealing strong electron-phonon interactions near a charge-density-wave instability that support its conventional superconductivity.

Contribution

It provides the first detailed density functional analysis of LaO$_{0.5}$F$_{0.5}$BiS$_{2}$, highlighting electron-phonon coupling and charge density wave proximity as key factors in its superconductivity.

Findings

Fermi surface nesting indicates charge density wave proximity.

Imaginary phonons suggest lattice instability near certain wave vectors.

Electron-phonon coupling constant $   0.85 supports conventional superconductivity.

Abstract

We discuss the electronic structure, lattice dynamics and electron-phonon interaction of newly discovered superconductor LaO$_{0.5}$F$_{0.5}$BiS$_{2}$ using density functional based calculations. A strong Fermi surface nesting at $\mathbf{k}$=($\pi $,$\pi $,0) suggests a proximity to charge density wave instability and leads to imaginary harmonic phonons at this $\mathbf{k}$ point associated with in-plane displacements of S atoms. Total energy analysis resolves only a shallow double-well potential well preventing the appearance of static long-range order. Both harmonic and anharmonic contributions to electron-phonon coupling are evaluated and give a total coupling constant $\lambda \simeq 0.85$ prompting this material to be a conventional superconductor contrary to structurally similar FeAs materials.