Peculiar properties of the Josephson junction at the transition from 0 to Pi state

TL;DR

This paper investigates the unique properties of Josephson junctions during the 0 to Pi transition, revealing a dominant second harmonic near the transition and predicting the nature of the transition based on barrier homogeneity.

Contribution

It provides a detailed analysis of the current-phase relation near the 0-Pi transition, highlighting the role of the second harmonic and effects of barrier modulation.

Findings

Second harmonic dominates near the 0-Pi transition.

Homogeneous barriers lead to a first order transition.

Barrier modulation can enable continuous transition and arbitrary phase states.

Abstract

It is demonstrated that in the diffusive superconductor-ferromagnet-superconductor (S/F/S) junctions the current-phase relation is practically sinusoidal everywhere except in a narrow region near the 0-Pi transition. In this region the second harmonic dominates the scenario of the 0-Pi transition. We predict a first order transition for the S/F/S junctions with a homogeneous F barrier. However, in real junctions a small modulation of the thickness of the barrier may favor the continious 0-Pi transition and the realisation of the Josephson junction with an arbitrary ground state phase difference. The performed calculations of the second harmonic amplitude provide a natural explanation of the recent contradictory results on the second harmonic measurements.