McMillan-Rowell tunneling spectroscopy in the Nb-Zr system

Abstract

We report the first full application of tunneling spectroscopy to a superconducting transition metal alloy: Nb 1− x Zr x at x = 0.25, corresponding to the maximum T c in the Nb-Zr system. The spectral function α 2 F(ω ) and related parameters, when compared to those for the Nb, confirm that the increase in T c from 9.22 K ( x = 0) to 10.8 K( x = 0.25) arises largely by softening of the effective phonon spectrum.