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

摘要

We discuss the electronic structure, lattice dynamics and electron-phononinteraction 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 waveinstability and leads to imaginary harmonic phonons at this $\mathbf{k}$ pointassociated with in-plane displacements of S atoms. Total energy analysisresolves only a shallow double-well potential well preventing the appearance ofstatic long-range order. Both harmonic and anharmonic contributions toelectron-phonon coupling are evaluated and give a total coupling constant$\lambda \simeq 0.85$ prompting this material to be a conventionalsuperconductor contrary to structurally similar FeAs materials.