1 research outputs found
Degenerate ground state and anomalous flux hysteresis in an YBa2Cu3O7 grain boundary r.f. SQUID
We report measurements of the flux hysteresis curves and trapped flux
distribution in an YBa2Cu3O7 r.f. 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.Comment: 10 pages, 7 figure