Enhancing superconductivity: Magnetic impurities and their quenching by magnetic fields

TL;DR

This paper explores how magnetic fields can suppress or enhance superconductivity by affecting magnetic impurities, revealing non-monotonic critical current behavior in superconducting wires and films.

Contribution

It introduces a theoretical analysis of the interplay between magnetic impurities and fields in superconductors, showing potential for field-enhanced superconductivity.

Findings

Critical current exhibits non-monotonic dependence on magnetic field.

Field polarization of impurities can lead to superconductivity enhancement.

Critical temperature decreases monotonically with field, but critical current can increase.

Abstract

Magnetic fields and magnetic impurities are each known to suppress superconductivity. However, as the field quenches (i.e. polarizes) the impurities, rich consequences, including field-enhanced superconductivity, can emerge when both effects are present. For the case of superconducting wires and thin films, this field-spin interplay is investigated via the Eilenberger-Usadel scheme. Non-monotonic dependence of the critical current on the field (and therefore field-enhanced superconductivity) is found to be possible, even in parameter regimes in which the critical temperature decreases monotonically with increasing field. The present work complements that of Kharitonov and Feigel'man, which predicts non-monotonic behavior of the critical temperature.