Minimal electronic models for superconducting BiS$_2$ layers

TL;DR

This paper develops minimal electronic models for the superconductor LaO$_{1-x}$F$_x$BiS$_2$, highlighting its band structure, Fermi surface topology, and potential pairing mechanisms based on first-principles calculations.

Contribution

It introduces simplified two-orbital models capturing the essential electronic features of BiS$_2$ layers, aiding understanding of superconductivity in this material.

Findings

Two-band models show nearly electron-hole symmetric bands.

Fermi surface topology changes around $x\,\sim 0.5$, increasing the density of states.

Quasi-one-dimensional character of bands suggests nesting-related pairing mechanisms.

Abstract

We construct minimal electronic models for a newly discovered superconductor LaO$_{1-x}$F$_x$BiS$_2$ ($T_c=$ 10.6K) possessing BiS$_2$ layers based on first principles band calculation. First, we obtain a model consisting of two Bi $6p$ and two S $3p$ orbitals, which give nearly electron-hole symmetric bands. Further focusing on the bands that intersect the Fermi level, we obtain a model with two $p$ orbitals. The two bands (per BiS$_2$ layer) have quasi-one-dimensional character with a double minimum dispersion, which gives good nesting of the Fermi surface. At around $x\sim 0.5$ the topology of the Fermi surface changes, so that the density of states at the Fermi level becomes large. Possible pairing states are discussed.