Pauli-Limited Superconductivity in Small Grains

TL;DR

This paper investigates how superconductivity in small metallic grains is affected by size, focusing on the interplay between Zeeman coupling and grain size, revealing that smaller grains can sustain higher magnetic fields.

Contribution

It provides a detailed mean-field phase diagram for Pauli-limited superconductivity in small grains, highlighting the size-dependent increase in critical Zeeman coupling.

Findings

Maximum Zeeman coupling increases as grain size decreases

Superconductivity disappears in ultra-small grains

Condensation energy per volume decreases with size

Abstract

We report on an exploration of the mean-field phase diagram for Pauli-limited superconductivity in small metallic grains. Emphasis is placed on the crossover from the ultra-small grain limit where superconductivity disappears to the bulk thin-film limit as the single-particle level spacing in the grain decreases. We find that the maximum Zeeman coupling strength compatible with superconductivity increases with decreasing grain size, in spite of a monotonically decreasing condensation energy per unit volume.