Anomalous in-plane anisotropy of the resistivity on single crystalline 60-K YBa2Cu3O7-δ in high magnetic fields

We have measured the in-plane anisotropy of the in-plane resistivity on 60-K YBa2Cu3O7-delta single crystals in magnetic fields parallel with the ab-plane. In high magnetic fields, the temperature dependence of the resistivity rho(T) for H perpendicular to I shows the jump near the zero-resistivity transition, while the rho(T) for Hparallel toI the gradual behavior. Furthermore, the transition temperature of the latter is lower than that of the former, which is inconsistent with the vortex dynamics induced by the Lorentz force. We discuss the observed anomalous behavior in terms of the phase transition of the Josephson vortex system. (C) 2003 Elsevier Science B.V. All rights reserved.