Electron tunneling spectroscopy of superconducting A15 V-Ga alloy films.

Abstract

The results of a tunneling study of the high-${T}_{c}$, A15 superconductor ${\mathrm{V}}_{3}$Ga are presented. The superconducting electron-phonon interaction spectral function ${\ensuremath{\alpha}}^{2}$F(\ensuremath{\omega}) is obtained for a set of samples with compositions spanning stoichiometry. These results are of particular interest since ${\mathrm{V}}_{3}$Ga is unusual among the high-${T}_{c}$, A15 superconductors in that single-phase material can be formed on either side of stoichiometry. The results demonstrate that increased weight of ${\ensuremath{\alpha}}^{2}$F(\ensuremath{\omega}) (or so-called mode softening) occurs at low energies as stoichiometry is approached either from above or below. Concomitantly ${\ensuremath{\omega}}_{\mathrm{log}}$ is found to show a minimum at stoichiometry. Interestingly, although ${T}_{c}$ is a symmetric function of composition around stoichiometry, ${\ensuremath{\omega}}_{\mathrm{log}}$ is asymmetric. Hence, some other factor beyond mode softening is playing a significant factor in the systematics of the high ${T}_{c}$'s exhibited by this superconductor as a function of composition.