Vortex quantum tunnelling versus thermal activation in ultrathin superconducting nanoislands

TL;DR

This paper compares quantum tunnelling and thermal activation as mechanisms for vortex entry and exit in ultrathin superconducting nanoislands, revealing quantum tunnelling's dominance in entry and thermal activation in exit.

Contribution

It provides a theoretical analysis of vortex entry and exit mechanisms, establishing criteria for crossover between quantum tunnelling and thermal activation based on system parameters.

Findings

Quantum tunnelling dominates vortex entry in most conditions.

Thermal activation is more probable for vortex exit.

Crossover criteria depend on magnetic field and system size.

Abstract

We consider two possible mechanisms for single-vortex fluctuative entry/exit through the surface barrier in ultrathin superconducting disk-shaped nanoislands made of Pb and consisting of just few monoatomic layers, which can be fabricated using modern techniques. We estimate tunnelling probabilities and establish criteria for the crossover between these two mechanisms depending on magnetic field and system sizes. For the case of vortex entry, quantum tunnelling dominates on the major part of the temperature/flux phase diagram. For the case of vortex exit, thermal activation turns out to be more probable. This nontrivial result is due to the subtle balance between the barrier height and width, which determine rates of the thermal activation and quantum tunneling, respectively.