Critical currents, proximity effect, and Josephson penetration depth in planar high-T/sub c/ Josephson junctions

Abstract

We have studied the temperature dependence of the critical current in planar high-T/sub c/ Josephson junctions fabricated in YBa/sub 2/Cu/sub 3/O/sub 7/ thin films by focused electron irradiation. We show that in the range of critical current densities spanning more than five orders of magnitude and temperature range 0.1<T/T/sub c//spl les/1, the critical current density j/sub c/ varies as (1-T/T/sub c/)/sup 2/. The T-dependence of the critical current I/sub c/, however, is affected by the transition from the narrow-junction to the wide-junction limit as j/sub c/ increases. An expression for the Josephson penetration depth in thin-film planar structures has been derived, and the value of magnetic field penetration depth in junction banks has been extracted from the I/sub c/(T) dependences. Some issues of the proximity effect associated with unconventional pairing symmetry in high-T/sub c/ superconductors are also discussed.