Imaging spontaneous currents in superconducting arrays of π-junctions
Author: ["Sergey M. Frolov","Micah J. A. Stoutimore","Trevis A. Crane","Dale J. Van Harlingen","Vladimir A. Oboznov","Valery V. Ryazanov","Adele Ruosi","Carmine Granata","Maurizio Russo"]
Publication: Nature Physics
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Abstract
A charge current can flow between two superconductors separated by a thin barrier. This phenomenon is the Josephson effect, which enables a current to tunnel at zero voltage1, typically with no phase shift between the superconductors in the lowest-energy state. Recently, Josephson junctions with ground-state phase shifts of π, proposed by theory three decades ago2, have been demonstrated3,4,5. In superconducting loops, π-junctions cause spontaneous circulation of persistent currents in zero magnetic field2, in analogy to spin-1/2 systems6. Here we use a scanning superconducting quantum interference device microscope7 to image the spontaneous zero-field currents in superconducting networks of temperature-controlled π-junctions with weakly ferromagnetic barriers3. We find an onset of spontaneous supercurrents at the 0–π transition temperature of the junctions, Tπ≈3 K. We image the currents in non-uniformly frustrated arrays consisting of cells with even and odd numbers of π-junctions. Such arrays are attractive model systems for studying the exotic phases of the two-dimensional XY-model8,9 and achieving scalable adiabatic quantum computers10.
Cite this article
Frolov, S., Stoutimore, M., Crane, T. et al. Imaging spontaneous currents in superconducting arrays of π-junctions. Nature Phys 4, 32–36 (2008). https://doi.org/10.1038/nphys780
