Josephson junction with magnetic-field tunable ground state

TL;DR

This paper investigates a magnetic-field tunable ground state in an asymmetric 0-pi Josephson junction with a negative second harmonic, demonstrating how an applied magnetic field influences its phase and critical current.

Contribution

It introduces a model for a Josephson junction with a tunable ground state via magnetic field, incorporating a negative second harmonic in the current-phase relation.

Findings

Magnetic field H induces an additional term in the current-phase relation.

The ground state can be tuned between different phases by varying H.

Critical current dependence on H reveals the ground state properties.

Abstract

We consider an asymmetric 0-pi Josephson junction consisting of 0 and pi regions of different lengths L_0 and L_pi. As predicted earlier this system can be described by an effective sine-Gordon equation for the spatially averaged phase psi so that the effective current-phase relation of this system includes a \emph{negative} second harmonic ~sin(2 psi). If its amplitude is large enough, the ground state of the junction is doubly degenerate psi=\pmvarphi, where varphi depends on the amplitudes of the first and second harmonics. We study the behavior of such a junction in an applied magnetic field H and demonstrate that H induces an additional term ~H cos(psi) in the effective current-phase relation. This results in a non-trivial ground state \emph{tunable} by magnetic field. The dependence of the critical current on H allows for revealing the ground state experimentally.