Effect of hydrostatic pressure on the electronic and superconducting properties of bismuthate superconductor: An <i>ab initio</i> study

The present study investigates the influence of hydrostatic pressure on the electronic structure and the electron–phonon coupling in Ba0.6K0.4BiO3 (BKBO) cubic superconductor using first-principles calculations. The increase in applied pressure increases the degree of orbital hybridization between Bi-s and O-pσ states. Also, suppression of oxygen hole is observed with increasing applied pressure, and Bi-s states play a more crucial role in the metallicity of the material. The study of lattice dynamics reveals that the cubic BKBO compound is dynamically stable up to an applied pressure of ∼7 GPa. The primary contribution to the overall electron–phonon coupling comes from the phonons associated with the oxygen bond stretching vibrations. With the increase in the hydrostatic pressure applied on the system, the phonon frequencies corresponding to oxygen bond stretching vibrations increase, leading to a decrease in electron–phonon coupling strength and, hence, the reduction in the superconducting Tc. The suppression of Tc can be attributed to the suppression of electronic density of states at the Fermi level. The superconducting parameters calculated using density functional theory within the generalized gradient approximation are underestimated compared to the experimental values. The implementation of the HSE06 hybrid functional enhances the electron–phonon coupling in the compound by incorporating the long-range Coulomb interaction in the system. It makes λ and Tc close to the experiments while maintaining the similar behavior of these superconducting properties under pressure as in the GGA calculations. These results highlight the exact role of nonlocal electronic correlation in the superconductivity in bismuthate.