Temporarily enhanced superconductivity from magnetic fields

TL;DR

This paper predicts that a sudden application of a magnetic field can temporarily enhance superconductivity, notably increasing supercurrent in Josephson junctions, due to interplay between Andreev reflection and spin effects.

Contribution

It introduces a novel theoretical prediction of transient superconductivity enhancement caused by abrupt magnetic fields and develops a method to solve the Usadel equation for arbitrary time-dependence.

Findings

Supercurrent can increase more than twentyfold temporarily.

The enhancement duration is in the nanosecond range.

A new method for ultrafast time-dependent analysis of superconductor heterostructures.

Abstract

Contrary to the expected detrimental influence on superconductivity when applying a magnetic field, we predict that the abrupt onset of such a field can temporarily strongly enhance the superconducting order parameter. Specifically, we find that the supercurrent in a Josephson junction with a normal metal weak link can increase more than twentyfold in this way. The effect can be understood from the interplay between the energy-dependence of Andreev reflection and the abrupt spin-dependent shift in the distribution functions for excitations in the system. The duration of the increase depends on the inelastic scattering rate in the system and is estimated to be in the range of nanoseconds. We demonstrate this by developing a method which solves the Usadel equation for an arbitrary time-dependence. This enables the study of ultrafast time-dependent physics in heterostructures combining superconductors with different types of materials.