Interplay between exchange interactions and charging effects in metallic grains

TL;DR

This paper investigates how exchange interactions and spin fluctuations influence Coulomb blockade phenomena in small superconducting grains, revealing that suppressed spin fluctuations enhance Coulomb blockade effects.

Contribution

It extends the standard charge-phase model by incorporating spin degrees of freedom, providing a more comprehensive understanding of charging effects in superconducting grains.

Findings

Suppressed spin fluctuations increase Coulomb blockade tendency.

Effective charging energy is influenced by exchange interactions.

Conductance is numerically calculated for large grain-lead coupling.

Abstract

We study the effect of the exchange interactions in small superconducting grains near the Coulomb blockade regime. We extend the standard description of the grain in terms of a single collective variable, the charge and its conjugated phase, to include the spin degree of freedom. The suppression of spin fluctuations enhances the tendency towards Coulomb blockade. The effective charging energy and conductance are calculated numerically in the regime of large grain-lead coupling.