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Coupling of two superconductors through a ferromagnet : evidence for a pi-junction

V. V. Ryazanov·V. A. Oboznov·A. Yu. Rusanov·A. V. Veretennikov·A. A. Golubov·J. Aarts
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Abstract

We report measurements of the temperature dependence of the critical current in Josephson junctions consisting of conventional superconducting banks of Nb and a weakly ferromagnetic interlayer of a Cu$_x$Ni$_{1-x}$ alloy, with $x$ around 0.5. With decreasing temperature $I_c$ generally increases, but for specific thicknesses of the ferromagnetic interlayer, a maximum is found followed by a strong decrease down to zero, after which $I_c$ rises again. Such a sharp cusp can only be explained by assuming that the junction changes from a 0-phase state at high temperatures to a $π$-phase state at low temperatures.

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V. V. Ryazanov, V. A. Oboznov, A. Yu. Rusanov, A. V. Veretennikov, A. A. Golubov, J. Aarts. 2000-08-24. Coupling of two superconductors through a ferromagnet : evidence for a pi-junction. https://doi.org/10.1103/physrevlett.86.2427

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