Superconductivity in 2D granular NbN

The systematics of superconductivity in 2D granular NbN are reported as a function of variable intergranular coupling strength Jgg′. The characteris tics of the resistive transition, the critical currents and the dynamical I‐V response are markedly altered by variations Jgg′. The results of this study are consistent with previous investigations of 2D granular NbN where three critical temperatures Tcg (superconducting transition of individual grains), Tcj (2D phase ordering transition) and T* (sudden increase in Ic) were identified. As the coupling Jgg′ decreases, the critical fluctuation region above Tcj increases in magnitude and in temperature span. Similarly, the temperature T* moves to lower temperatures relative to Tcj as Jgg′ decreases. Examination of the I‐V response curves revealed a hitherto unidentified characteristic temperature Ts which marks a change in the dynamic response of these 2D NbN films.