Effect of La Doping on the Electronic Structure of BiS$_{2}$-Based Superconductor Sr$_{1-x}$La$_{x}$FBiS$_{2}$

Abstract

By means of first-principles calculations, we have systematically studied the La doping effect for the recently discovered layered BiS$_{2}$-based superconductor Sr$_{1-x}$La$_{x}$FBiS$_{2}$ ($x = 0$–0.7). For the electronic structure, we obtained the band structure, density of states (DOS), and Fermi surface (FS) at different doping levels. The parent compound SrFBiS$_{2}$ is a semiconductor with a gap of 0.88 eV. The substitution of Sr by La dopes electrons and turns the system from a semiconductor to a metal. The band structure and the FS topology also change obviously with the increasing of doping level. Good FS nesting at the wave vector ($\pi$, $\pi$, 0 ) has been found at certain doping levels, suggesting a proximity to charge-density-wave instability. Particularly, the doping dependence of DOS at the Fermi level resembles the available experimental variation of $T_{\mathrm{c}}$ as the function of x, indicating that it may be a conventional phonon-mediated superconductor. This was further proved by electron–phonon coupling calculation. Therefore, similar to LaO$_{1-x}$F$_{x}$BiS$_{2}$, our results suggest another example of superconductor derived from doped semiconductor.