JOSEPHSON FLUX-FLOW RESONANCES IN OVERDAMPED LONG YBA2CU3O7 GRAIN-BOUNDARY JUNCTIONS

A resonance structure was observed in the current-voltage curves of overdamped long 0-32°[001]-tilt YBa2Cu3O7 bicrystal grain-boundary junctions (GBJ's), and is attributed to a Josephson flux-flow resonance. The voltage position of the resonance moves almost linearly from 0.5 to 2 mV with an applied magnetic field. From this linear dependence and using the London penetration depth λL=140 nm, we determined the ratio between the effective dielectric thickness and the relative dielectric constant t/r0.3 nm, and the quasiparticle loss coefficient α=1.3 at 16 K for a 30-μm long junction. The loss increases with temperature and no resonance was seen at 77 K. The perturbed sine-Gordon equation was used for modeling long GBJ's. Simulations support the experimental observation that Josephson vortices can propagate unidirectionally in an overdamped, homogeneous junction up to α2. © 1995 The American Physical Society.