Nonlinear resistivity in a d-wave superconductor YBa2Cu4O8 of sub-micron scale grains

Abstract

The d-wave ceramic YBa2Cu4O8 superconductor composed of sub-micron size grains is considered as random Josephson-coupled network of 0 and π junctions and shows successive phase transitions. The upper transition occurs inside each grain at Tc1 = 82 K and the lower transition occurs among the grains at Tc2 = 66 K. We measured the temperature dependence of the current-voltage characteristics of the ceramic YBa2Cu4O8 and derived the linear and nonlinear resistivity. The nonlinear resistivity ρ2 and ρ4 have finite values between Tc1 and Tc2 and have the peak at the same temperature Tp = 70 K above Tc2. The result agrees with the theoretical one obtained by Li and Domínguez. They interpreted Tp as the crossover temperature from the normal state phase to a chiral paramagnetic one.