Dynamics of semifluxons in Nb long Josephson 0-pi junctions

TL;DR

This paper experimentally investigates the dynamics of semifluxons in long Nb Josephson 0-pi junctions, demonstrating controllable phase discontinuities and observing fractional vortices and zero-field steps.

Contribution

It introduces a method to create arbitrary phase discontinuities in Nb Josephson junctions and studies the resulting fractional vortex dynamics experimentally.

Findings

Creation of controllable phase discontinuities using current injectors.

Observation of fractional Josephson vortices and their dynamics.

Detection of half-integer zero-field steps in current-voltage characteristics.

Abstract

We propose, implement and test experimentally long Josephson 0-pi junctions fabricated using conventional Nb-AlOx-Nb technology. We show that using a pair of current injectors, one can create an arbitrary discontinuity of the Josephson phase and in particular a pi-discontinuity, just like in d-wave/s-wave or in d-wave/d-wave junctions, and study fractional Josephson vortices which spontaneously appear. Moreover, using such junctions, we can investigate the \emph{dynamics} of the fractional vortices -- a domain which is not yet available for natural 0-pi-junctions due to their inherently high damping. We observe half-integer zero-field steps which appear on the current-voltage characteristics due to hopping of semifluxons.