Degenerate ground state and anomalous flux hysteresis in an YBa2Cu3O7 grain boundary rf SQUID

C. H. Gardiner, R. A. M. Lee, J. C. Gallop, A. Y. Tzalenchuk, J. C. Macfarlane, L. Hao

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We report measurements of the flux hysteresis curves and trapped flux distribution in an YBa2Cu3O7 rf SQUID containing two closely spaced grain boundary Josephson junctions in parallel. Broadening of the flux distribution from T = 15 K to 30 K is followed by a bifurcation at T = 35 K which corresponds to a degenerate ground state. Above T approximate to 40 K the bifurcation disappears, the flux distribution narrows significantly and small secondary loops appear in the hysteresis curves. This behaviour can be modelled qualitatively if we assume a temperature dependent second harmonic term in the current-phase relationship of the junctions.
Original languageEnglish
Pages (from-to)S234-S240
JournalSuperconductor Science and Technology
Issue number5
Publication statusPublished - 2004

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