Correlation-enhanced electron-phonon coupling and superconductivity in (Ba,K)SbO3 superconductors

The electronic structure, lattice dynamics, and electron-phonon coupling (EPC) of the recently discovered $(\mathrm{Ba},\mathrm{K})\mathrm{Sb}{\mathrm{O}}_{3}$ superconductors are investigated by first-principles calculations. The EPC of $(\mathrm{Ba},\mathrm{K})\mathrm{Sb}{\mathrm{O}}_{3}$ is significantly enhanced by considering nonlocal electronic correlation using the Heyd-Scuseria-Ernzerhof hybrid exchange-correlation functional (HSE06). The EPC strength \ensuremath{\lambda} of ${\mathrm{Ba}}_{0.35}{\mathrm{K}}_{0.65}{\mathrm{SbO}}_{3}$ is strongly increased from 0.33 in local-density approximation calculations to 0.59 in HSE06 calculations, resulting in a superconducting transition temperature ${T}_{c}$ of about 14.9 K, which is in excellent agreement with experimental value of \ensuremath{\sim}15 K. Our findings suggest $(\mathrm{Ba},\mathrm{K})\mathrm{Sb}{\mathrm{O}}_{3}$ are extraordinary conventional superconductors, where nonlocal electronic correlation expands the bandwidth, enhances the EPC, and boosts the ${T}_{c}$. Moreover, we find both \ensuremath{\lambda} and ${T}_{c}$ depend crucially on the K-doping level for $(\mathrm{Ba},\mathrm{K})\mathrm{Sb}{\mathrm{O}}_{3}$ and $(\mathrm{Ba},\mathrm{K})\mathrm{Bi}{\mathrm{O}}_{3}$ compounds. $(\mathrm{Ba},\mathrm{K})\mathrm{Sb}{\mathrm{O}}_{3}$ have stronger EPC strength and higher ${T}_{c}$ than those of $(\mathrm{Ba},\mathrm{K})\mathrm{Bi}{\mathrm{O}}_{3}$ at the same K-doping level.