Nucleation of Superconductivity in Thin Type-I Foils

TL;DR

This paper investigates the nucleation process of superconductivity in thin type-I foils under decreasing magnetic fields, revealing the roles of critical fields $H_{c3}$ and $H_{c2}$ and providing Ginzburg-Landau parameters.

Contribution

It provides experimental observations of superconductivity nucleation at $H_{c3}$ and reinitiation at $H_{c2}$ in thin foils, with derived Ginzburg-Landau parameters.

Findings

Superconductivity nucleates at $H_{c3}$ during decreasing magnetic field.

Reinitiation of superconductivity occurs at $H_{c2}$.

Ginzburg-Landau parameters are about half of tabulated values.

Abstract

The nucleation of the superconductive phase in macroscopic type-I foils in a slow, continuously decreasing perpendicular magnetic field is observed to first occur at the field $H_{c3}$, and reinitiate at $H_{c2}$. The observed variation of $H_{c2}$ with temperature further yields Ginzburg-Landau parameters for the materials approximately a factor 2 below tabulations, consistent with previous determinations in small grains.