Current-phase relation in Josephson junction coupled with a magnetic dot

TL;DR

This paper investigates how a small ferromagnetic particle influences the current-phase relation in a short Josephson junction, revealing vortex-induced phase shifts and the potential for tuning the junction's ground state phase difference.

Contribution

It demonstrates the impact of vortex pairs on the phase difference in Josephson junctions and explores how to tune this phase for potential applications.

Findings

Vortex-antivortex pairs induce a fixed phase drop $$ in the junction.

The ground state phase difference $$ depends on vortex configuration.

Tuning of the ground state phase difference is possible.

Abstract

The current-phase relation (CPR) for a short Josephson junction placed in the nonuniform field of a small ferromagnetic particle is studied. The effect of the particle produced on the junction appears to be strong due to the formation of the pair of oppositely directed Abrikosov vortices which pierce the thin film superconducting electrode and cause a small--scale inhomogeneity of Josephson phase difference. The induced phase difference inhomogeneity is shown to result in the nonzero fixed phase drop $\phi_0$ across the junction. The equilibrium value $\phi_0$ corresponding to the ground state of the junction depends the configuration of the vortex--antivortex pair. The possibility to tune the ground state phase difference $\phi_0$ is discussed.