Multiband superconductivity in $\mathrm{Bi}{\mathrm{S}}_2$-based layered compounds

Abstract

A mean-field treatment is presented of a square lattice two-orbital-model for $\mathrm{Bi}{\mathrm{S}}_2$ 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 ($\eta ={\mathrm{V}}_{\mathrm{XX}}/{\mathrm{V}}_{\mathrm{XY}}$) and electron doping $x$. With the help of a quantity we call orbital-mixing ratio, denoted as $R(\varphi )$, the phase diagram is analyzed using a simple and intuitive picture based on how $R(\varphi )$ varies as electron doping increases. The predictive power of $R(\varphi )$ suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.

23 pages, 8 figures

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