Non-ideal artificial phase discontinuity in long Josephson 0-kappa-junctions

TL;DR

This paper explores creating and studying arbitrary phase discontinuities in long Josephson junctions using current injectors, revealing deviations from ideal behavior due to finite injector size and confirming findings through numerical simulations.

Contribution

It introduces a method to generate arbitrary phase discontinuities in long Josephson junctions and analyzes the effects of finite injector size on their properties.

Findings

Finite injector size causes deviations from ideal junction behavior.

Numerical simulations accurately reproduce experimental deviations.

Calibration procedures for injectors are detailed.

Abstract

We investigate the creation of an arbitrary $\kappa$-discontinuity of the Josephson phase in a long Nb-AlO_x-Nb Josephson junction (LJJ) using a pair of tiny current injectors, and study the formation of fractional vortices formed at this discontinuity. The current I_inj, flowing from one injector to the other, creates a phase discontinuity kappa ~ I_inj. The calibration of injectors is discussed in detail. The small but finite size of injectors leads to some deviations of the properties of such a 0-kappa-LJJ from the properties of a LJJ with an ideal kappa-discontinuity. These experimentally observed deviations in the dependence of the critical current on I_inj$ and magnetic field can be well reproduced by numerical simulation assuming a finite injector size. The physical origin of these deviations is discussed.