31 research outputs found
The Influence of the Second Harmonic in the Current-Phase Relation on the Voltage-Current Characteristic of high TC DC SQUID
A theory for the voltage-current characteristic in high TC DC SQUIDs, which
accounts for a second harmonic in the junction current-phase relation, is
developed. The comparison with experiment is performed. It is shown that if the
second harmonic is prevailed, the theory can explain the large deviations of
the experimental voltage modulation from theoretical predictions and computer
simulations based on conventional sinusoidal current-phase relation.Comment: Eq. 13 is correcte
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