Phase Diagram and Upper Critical Field of Homogeneously Disordered Epitaxial 3-Dimensional NbN Films

Abstract

We report the evolution of superconducting properties with disorder, in 3-dimensional homogeneously disordered epitaxial NbN thin films. The effective disorder in NbN is controlled from moderately clean limit down to Anderson metal–insulator transition by changing the deposition conditions. We propose a phase diagram for NbN in temperature-disorder plane. With increasing disorder, we observe that as k_Fl→1 the superconducting transition temperature (T_c) and normal state conductivity in the limit T→0 (σ₀) go to zero. The phase diagram shows that in homogeneously disordered 3-D NbN films, the metal–insulator transition and the superconductor–insulator transition occur at a single quantum critical point, k_Fl∼1.