Vibrational Density-of-States, Isotope effect, and Superconductivity in Ba1-xKxBiO3 Cubic Oxides

Abstract

Vibrational density-of-states of insulating BaBiO3 in orthorhombic phase and superconducting Ba0.6K0.4BiO3 in cubic phase are studied using the molecular dynamics (MD) method. The MD results are compared with the recent inelastic neutron scattering and electron tunneling experiments. The exponent of the oxygen isotope effect is calculated from the first moment of the phonon density-of-states (the weak coupling limit) and from the solution of Eliashberg gap equations. Results are compared with isotope effect experiments. Evidence based on inelastic neutron scattering, tunneling, and isotope effect experiments when combined with the MD calculations suggest that this material is a normal weak coupling BCS superconductor with strong coupling of the carriers to high energy oxygen phonons.