Dynamic properties and nonequilibrium processes in electron-beam scribed $YBa2Cu3O7$ Josephson junctions

We present a detailed characterization of the dynamic properties of proximity-coupled Josephson junctions in $YBa2Cu3O7$ fabricated by electron-beam scribing. A full description of the low-temperature behavior includes nonequilibrium processes in the normal barrier as well as wide-junction effects resulting from the planar geometry. Above ∼40 K these junctions obey the standard (equilibrium) resistively-shunted junction (RSJ) model in applied magnetic field. At lower temperatures, the volt–ampere V(I) curves develop a temperature-dependent “excess critical current,” saturating at 0.5–0.75 of the total critical current. Below ∼10 K hysteresis is observed. The observed temperature dependence and magnitude of the excess current and hysteresis are qualitatively consistent with published calculations based on the time-dependent Ginzburg–Landau equations. At low temperatures, the V(I) curves in applied field deviate significantly from the RSJ model, which we attribute to wide-junction behavior with a nonuniform bias-current distribution.