Energy gap of the high field superconductor NbZr

Abstract

We report the first full application of tunneling spectroscopy to a superconducting transition metal alloy: Nb1−xZrx at x = 0.25, corresponding to the maximum Tc in the Nb-Zr system. The spectral function α2 F(ω) and related parameters, when compared to those for the Nb, confirm that the increase in Tc from 9.22 K (x = 0) to 10.8 K(x = 0.25) arises largely by softening of the effective phonon spectrum.