Surface superconducting states and paramagnetism in mesoscopic superconductors

TL;DR

This paper investigates surface superconducting states and paramagnetism in mesoscopic superconductors using Ginzburg-Landau theory, revealing how geometry influences magnetic properties and phase transitions.

Contribution

It provides a detailed analysis of the temperature-dependent critical fields and magnetic responses in small ring-like superconductors, highlighting the role of geometry and phase transitions.

Findings

Paramagnetism appears in small parts of the phase diagram for certain geometries.

Inner parts of the ring exhibit positive magnetic moments.

Order parameter profiles change across first-order transition lines.

Abstract

In the framework of the Ginzburg-Landau equation, the temperature dependence of the upper critical field of small ring-like superconductors is studied. At equilibrium small parts of the phase diagram show paramagnetism for width / radius ratios below 0.85. Their number and extension increase with the size of the hole. In these regions, only the inner part of the ring shows a positive magnetic moment. The order parameter density profile appears to change, when crossing a first order transition line, which separates different angular momentum values, and we clarify the relationship between the localization of superconductivity nucleation and paramagnetism of those samples.