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Half-integer Shapiro steps at the 0-pi crossover of a ferromagnetic Josephson junction

H. Sellier·C. Baraduc·F. Lefloch·R. Calemczuk
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Abstract

We investigate the current-phase relation of S/F/S junctions near the crossover between the 0 and the pi ground states. We use Nb/CuNi/Nb junctions where this crossover is driven both by thickness and temperature. For a certain thickness a non-zero minimum of critical current is observed at the crossover temperature. We analyze this residual supercurrent by applying a high frequency excitation and observe the formation of half-integer Shapiro steps. We attribute these fractional steps to a doubling of the Josephson frequency due to a sin(2*phi) current-phase relation. This phase dependence is explained by the splitting of the energy levels in the ferromagnetic exchange field.

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H. Sellier, C. Baraduc, F. Lefloch, R. Calemczuk. 2004-06-10. Half-integer Shapiro steps at the 0-pi crossover of a ferromagnetic Josephson junction. https://doi.org/10.1103/physrevlett.92.257005

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