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 magnetic 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-ohmic behavior. Below H*(T), the V(I) curves are described by V/I is similar 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 flux creep energy barriers at any temperature and magnetic field are extracted. These data are used to calculate the magnetoresistivity curves rho(T, H) which compare very favorably with the experimental data over 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 creep and vortex glass. We have not found evidence of the phase transition predicted in the latter case. The upper part of the resistive transition can be described in terms of the field enhanced 2D fluctuations. However, the significance of this analysis is questioned.