ANISOTROPIC AND THERMALLY ACTIVATED RESISTIVE BEHAVIOR IN ND1.85CE0.15CUO4-DELTA

An anisotropic-field-induced resistive transition has been measured for highly c-axis-oriented Nd1.85Ce0.15CuO4- thin films as a function of a magnetic field H parallel and perpendicular to the c axis. It is found that the observed resistivity below Tc scales as (T)=0 exp{-U(H)[1-T/Tc(H)]n/kBT} with n=2 for Hc and n=3 for Hc. This resistive behavior is explained by thermally activated flux motion based on a depinning model for flux lines in a quasi-two-dimensional superconductor. Numerical fitting leads to an estimation of the upper critical field, which results in a straight H-T phase boundary in quite a wide range below Tc with upward deviation at lower temperatures. © 1990 The American Physical Society.