Half-integer Shapiro Steps in Strong Ferromagnetic Josephson Junctions

TL;DR

This paper reports the experimental detection of half-integer Shapiro steps in strong ferromagnetic Josephson junctions, revealing complex phase relations influenced by coexisting 0- and pi-states across a broad temperature range.

Contribution

It provides the first experimental observation of half-integer Shapiro steps in strong ferromagnetic Josephson junctions and links these to coexisting 0- and pi-states.

Findings

Half-integer Shapiro steps are observed in Nb-NiFe-Nb junctions.

The steps are stable from 4 to 7 K.

The results suggest coexistence of 0- and pi-states in the junctions.

Abstract

We report the experimental observation of half-integer Shapiro steps in the strong ferromagnetic Josephson junction (Nb-NiFe-Nb) by investigating the current-phase relation under radiofrequency microwave excitation. The half-integer Shapiro steps are robust in a wide temperature range from T = 4 to 7 K. The half-integer Shapiro steps could be attributed to co-existence of 0- and pi-states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the2 NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization of the Nb/NiFe/Nb junction.