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Degenerate ground state and anomalous flux hysteresis in an YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> grain boundary rf SQUID

By C.H. Gardiner, R.A.M. Lee, J.C. Gallop, A.Ya. Tzalenchuk, J.C. Macfarlane and L. Hao


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 ≈ 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

Publisher: IOP Publishing
Year: 2004
DOI identifier: 10.1088/0953-2048/17/5/028
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