Electronic structure of carbosulfide superconductors

Abstract

We present electronic band structure calculations and x-ray emission and photoelectron measurements of the recently discovered van der Waals\char21{}type layered superconductors ${\mathrm{Nb}}_{2}{\mathrm{S}}_{2}\mathrm{C}$ and ${\mathrm{Cu}}_{2∕3}{\mathrm{Nb}}_{2}{\mathrm{S}}_{2}\mathrm{C}$. Good agreement between our local partial density-of-states calculations and our experimental x-ray emission measurements of the constituents as well as between calculated and experimental $E(\mathbf{k})$ dispersion curves is found for ${\mathrm{Nb}}_{2}{\mathrm{S}}_{2}\mathrm{C}$. For ${\mathrm{Cu}}_{2∕3}{\mathrm{Nb}}_{2}{\mathrm{S}}_{2}\mathrm{C}$, we observe a strong interaction between Cu $3d$ and S $3s3p$ states that is responsible for shifting the S $3s3p$ states toward to the bottom of the valence band.