Possible pi-phase shift at interface of two pnictides with antiphase s-wave pairing

TL;DR

This paper investigates the Josephson junction behavior between two Fe-pnictides with anti-phase s-wave pairing, revealing conditions for pi-phase shifts that explain observed flux quantum transitions in related superconducting loops.

Contribution

It introduces a theoretical model predicting pi-phase shifts at Fe-pnictide interfaces based on junction thickness and orientation, explaining experimental flux quantum phenomena.

Findings

Pi-phase shift occurs with thick junction barriers and specific orientations.

The theory explains half-integer flux quantum transitions in Nb/Fe-pnictide loops.

Intergrain junctions are key to the observed phase shifts.

Abstract

We examine the nature of Josephson junction between two identical Fe-pnictides with anti-phase s-wave pairing. pi-phase shift is found if the junction barrier is thick and the two Fe-pnictides are oriented in certain directions relative to the interface. Our theory provides a possible explanation for the observed half integer flux quantum transitions in a niobium/polycrystal NdFeAsO loop, and attributes the pi-phase shift to intergrain junctions of Fe-pnictides.