Proximity effect model of ultra-narrow NbN strips

TL;DR

This paper introduces a universal proximity effect model for ultra-narrow NbN superconducting strips, describing their transition from superconducting to normal states based on their width and edge damage, supported by experimental data.

Contribution

It presents a new proximity effect model for narrow NbN strips, linking their superconducting behavior to their width and edge damage, validated by systematic experiments.

Findings

Critical current dependence on strip width and temperature.

Transition from Meissner to vortex state at specific magnetic fields.

Gradual evolution of superconducting properties with width.

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 ${\mu}$m, which are all smaller than the Pearl's length, demonstrates gradual evolution of the temperature dependence of the critical current with the change of the strip width.