Electron-Phonon Coupling Constant of the Oxide Superconductor BaPb_1−xBi_xO₃

Abstract

By means of measurements of the ultrasonic attenuation and velocity change, we have derived the magnitude of McMillan’s parameter λ of the oxide superconductor BaPb_1−xBi_xO₃ (x=0.20–0.25). In this derivation we have assumed that the interaction between the conduction electrons and the sound waves is of the deformation potential type and the magnetic field dependent part of the attenuation at T<T_c is contributed from the normal conduction electrons. The value obtained is λ∼0.85 for the sample with T_c=10.5 K. It is shown that a relatively large deformation potential constant |V_d|=2.0 eV, which is 2.7 times larger than the Fermi energy and comes into λ in square, counterbalances the small density of states of this material and consequently leads to a reasonably large magnitude of λ for this rather semimetallic material.