Effects of thermal fluctuations on the magnetic behavior of mesoscopic superconductors

TL;DR

This paper investigates how thermal fluctuations influence the magnetic properties of mesoscopic superconductors, revealing distinct behaviors in low- and high-temperature superconductors related to vortex dynamics and magnetization.

Contribution

It provides a comparative analysis of thermal fluctuation effects on vortex behavior and magnetization in low- and high-$T_c$ mesoscopic superconductors using the Ginzburg number as a parameter.

Findings

Meta-stable states have long half-life in low-$T_c$ superconductors, causing hysteresis.

High-$T_c$ superconductors exhibit frequent vortex entry/exit, reducing magnetization.

Vortex state probabilities and fluctuations depend on magnetic field and temperature.

Abstract

We study the influence of thermal fluctuations on the magnetic behavior of square mesoscopic superconductors. The strength of thermal fluctuations are parameterized using the Ginzburg number, which is small ($G_i \approx 10^{-10}$) in low-$T_c$ superconductors and large in high-$T_c$ superconductors ($G_i \approx 10^{-4}$). For low-$T_c$ mesoscopic superconductors we found that the meta-stable states due to the surface barrier have a large half-life time, which leads to the hysteresis in the magnetization curves as observed experimentally. A very different behavior appears for high-$T_c$ mesoscopic superconductors where thermally activated vortex entrance/exit through surface barriers is frequent. This leads to a reduction of the magnetization and a non-integer average number of flux quanta penetrating the superconductor. The magnetic field dependence of the probability for the occurrence of the different vortex states and the fluctuations in the number of vortices are studied.