A first-principles study on the electronic structure of BaSbO3 and electron-phonon coupling in K-doped superconducting antimonate

Abstract

The present study attempts to explore the electronic structure of pure BaSbO₃ and the effect of K-doping on the electronic structure and electron-phonon interaction in K-doped barium antimonate (BKSO) superconductor using the first-principles method. A strong orbital hybridization is found to occur between Sb-s and O-p_σ states, which is enhanced in the collapsed octahedra of pure BaSbO₃. Also, the degree of the hybridization increases with the increase in K concentration in the system. O K-edge XANES study reveals that the self-doped holes do not reside on the ligand oxygen in the sp_σ antibonding orbital. This suppression of oxygen hole in the antimonate is consistent with the positive charge transfer energy of the systems. With increasing K doping in the superconducting antimonate, the electron-phonon coupling strength in the materials decreases. The coupling between the electrons and the phonons corresponding to the oxygen bond-stretching vibrations has the major contribution to the electron-phonon coupling and hence, superconductivity in the systems. The DFT-GGA calculated values of λ and T_c, using the Migdal-Eliashberg formalism, are heavily underestimated compared to the experimental values. The inclusion of long-range interaction and screening in the calculations by using HSE06 hybrid functional significantly enhanced the superconducting parameters, resulting in a T_c value of 14.611 K for the material with x = 0.65, which is quite close to the experimental value of 15 K. This study also concludes that the suppression of the oxygen hole in the conduction band serves as a crucial factor for having a lower T_c of antimonate compared to that of superconducting bismuthate.