Half-integer Shapiro steps in strong ferromagnetic Josephson junctions
Yunyan Yao, Ranran Cai, See‐Hun Yang, Wenyu Xing, Yang Ma, Michiyasu Mori, Yuan Ji, Sadamichi Maekawa, X. C. Xie, Wei Han
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 radio-frequency 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 the coexistence of 0 and $\ensuremath{\pi}$ states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization of the Nb/NiFe/Nb junction.