# Multiband superconductivity in ${\rm BiS_2}$-based layered compounds

## TL;DR

This paper presents a mean-field analysis of a two-orbital model for ${\rm BiS_2}$-based compounds, revealing a complex phase diagram of intra- and inter-orbital superconductivity influenced by doping and coupling ratios.

## Contribution

It introduces the orbital-mixing ratio $R(\phi)$ as a new tool to analyze multiband superconductivity in BCS-like materials.

## Key findings

- Rich phase diagram with various superconducting states
- Orbital-mixing ratio $R(\phi)$ effectively characterizes phase transitions
- Potential for $R(\phi)$ to guide analysis of multiband superconductors

## Abstract

A mean-field treatment is presented of a square lattice two-orbital-model for ${\rm BiS_2}$ taking into account intra- and inter-orbital superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between the couplings of electrons in the same and different orbitals (${\rm \eta= V_{XX}/V_{XY}}$) and electron doping $x$. With the help of a quantity we call orbital-mixing ratio, denoted as $R(\phi)$, the phase diagram is analyzed using a simple and intuitive picture based on how $R(\phi)$ varies as electron doping increases. The predictive power of $R(\phi)$ suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.