Electron-Phonon Coupling Constant of the Oxide Superconductor BaPb1-xBixO3

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- x Bi x O 3 ( 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.