Proximity effect model of ultranarrow NbN strips

Abstract

We show that narrow superconducting strips in superconducting (S) and normal (N) states are universally described by the model presenting them as lateral NSN proximity systems in which the superconducting central band is sandwiched between damaged edge bands with suppressed superconductivity. The width of the superconducting band was experimentally determined from the value of magnetic field at which the band transits from the Meissner state to the static vortex state. Systematic experimental study of 4.9-nm-thick NbN strips with widths in the interval from 50 nm to 20 mum, which are all smaller than the Pearl length, demonstrates gradual evolution of the temperature dependence of the critical current with the change of the strip width.