Correlation-enhanced electron-phonon coupling and superconductivity in (Ba ,K ) Sb O3 superconductors

The electronic structure, lattice dynamics, and electron-phonon coupling (EPC) of the recently discovered (Ba ,K ) Sb O₃ superconductors are investigated by first-principles calculations. The EPC of (Ba ,K ) Sb O₃ is significantly enhanced by considering nonlocal electronic correlation using the Heyd-Scuseria-Ernzerhof hybrid exchange-correlation functional (HSE06). The EPC strength λ of Ba_0.35K_0.65SbO₃ 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 ∼15 K. Our findings suggest (Ba ,K ) Sb O₃ are extraordinary conventional superconductors, where nonlocal electronic correlation expands the bandwidth, enhances the EPC, and boosts the T_c. Moreover, we find both λ and T_c depend crucially on the K-doping level for (Ba ,K ) Sb O₃ and (Ba ,K ) Bi O₃ compounds. (Ba ,K ) Sb O₃ have stronger EPC strength and higher T_c than those of (Ba ,K ) Bi O₃ at the same K-doping level.