THE RESISTIVE TRANSITION OF A SM1.85CE0.15CUO4-Y SINGLE-CRYSTAL

Current-voltage V(I) characteristics and the magnetoresistivity rho(T, H) have been measured for a Sm1.85Ce0.15CuO4-y single crystal in magn etic fields parallel to the c-axis. We have found that a well defined line H(T) exists in the H-T plane which separates ohmic from non-ohmi c behavior. Below H(T), the V(I) curves are described by V/I is simil ar to exp(-U(T, H, I)/k(B)T) where U(T, H, I) is similar to U(T, H)ln( I0/I). From the analysis of the V(I) characteristics, the effective fl ux creep energy barriers at any temperature and magnetic field are ext racted. These data are used to calculate the magnetoresistivity curves rho(T, H) which compare very favorably with the experimental data ove r less-than-or-equal-to 80%rho(n) of the resistive transition. The U(I ) is similar to ln I dependence, indicating the elastic nature of the flux creep process, is predicted by some recent theories: collective c reep and vortex glass. We have not found evidence of the phase transit ion predicted in the latter case. The upper part of the resistive tran sition can be described in terms of the field enhanced 2D fluctuations . However, the significance of this analysis is questioned.