Exponential H and T decay of the critical current density in YBa2Cu3O7√/sub δ/ single crystals

We report magnetic measurements on single crystals of YBa2Cu3O7√/sub δ/. The magnetic critical current density in the Cu-O basal planes (1.5 x 106 Acm2 at 4.2 K) decreases exponentially with temperature as well as with field for Tapprox. >50 K. This is ascribed to current tunneling through micro- Josephson-junctions. The behavior is radically different from that associated with macrojunctions typical of ''granular'' samples. It is argued that the anisotropy and the T-H anomalous behavior of J/sub c/ are connected with the T dependence and the anisotropy of both the coherence length and the electron mean free path