Spontaneous currents in Josephson devices

Abstract

The unconventional Josephson coupling in a ferromagnetic weak link between d-wave superconductors is studied theoretically. For strong ferromagnetic barrier influence, the unconventional coupling, with ground state phase difference across the link 0<φgs<~π, is obtained at small crystal misorientation of the superconducting electrodes, in contrast to the case of normal metal barrier, where it appears at large misorientations. In both cases, with decreasing temperature there is an increasing range of misorientations, where φgs varies continuously between 0 and π. When the weak link is a part of a superconducting ring, this is accompanied by the flow of spontaneous supercurrent, of intensity which depends (for a given misorientation) on the reduced inductance l=2πLIc(T)/Φ0, and is nonzero only for l greater than a critical value. For l≫1, another consequence of the unconventional coupling is the anomalous quantization of the magnetic flux.

Source-reported materials — not catalogue approval

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