Thermal suppression of surface barrier in ultrasmall superconducting structures

TL;DR

This paper analyzes how thermal effects can suppress the surface barrier in nanoscale low-temperature superconductors, explaining experimental observations of vortex behavior without hysteresis.

Contribution

It provides an analytical model for vortex surface barrier suppression via thermal activation, applicable to nanosized superconducting structures.

Findings

Thermally activated vortex entry times are much shorter than 1 second.

Thermal suppression of the surface barrier is feasible in nanoscale low-$T_c$ superconductors.

The model aligns with recent experimental results on vortex dynamics.

Abstract

In the recent experiment by Cren \textit{et al.} [Phys. Rev. Lett. \textbf{102}, 127005 (2009)], no hysteresis for vortex penetration and expulsion from the nano-island of Pb was observed. In the present paper, we argue that this effect can be associated with the thermoactivated surmounting of the surface barrier by a vortex. The typical entrance (exit) time is found analytically from the Fokker-Planck equation, written in the form suitable for the extreme vortex confinement. We show that this time is several orders of magnitude smaller than 1 second under the conditions of the experiment considered. Our results thus demonstrate a possibility for the thermal suppression of the surface barrier in nanosized low-$T_{c}$ superconductors. We also briefly discuss other recent experiments on vortices in related structures.