Tunneling studies in a homogeneously disordered s-wave superconductor: NbN

Abstract

We report the evolution of superconducting properties as a function of disorder in epitaxial NbN thin films grown on (100) MgO substrates. The effective disorder in these films encompasses a large range, with k_Fl∼1.38–8.77. Tunneling measurements reveal that for films with large disorder the superconducting transition temperature is not associated with a vanishing of the superconducting energy gap but with a large broadening of the superconducting density of states. Our results provide strong evidence of the loss of superconductivity via phase fluctuations in a homogeneously disordered s-wave superconductor.