Analysis of fluctuation conductivity in Y$_{0.5}$Cd$_{0.5}$Ba$_2$Cu$_3$O$_{7-\delta}$

A study was made of the influence of substitution of up to 50% of yttrium for cadmium in YBa$_2$Cu$_3$O$_{7-\delta}$ polycrystals on the mechanism of formation of excess conductivity. It has been established that such a substitution led to a significant increase in the resistivity of Y$_{0.5}$Cd$_{0.5}$Ba$_2$Cu$_3$O$_{7-\delta}$, and the value of the critical transition temperature $T_c$ to the superconducting state decreases. The mechanism of formation of fluctuation conductivity $(T)$ near $T_c$ is considered within the framework of the Aslamazov–Larkin theory. The Ginzburg temperature, the critical temperature in the mean field approximation, and the 3D–2D crossover temperature were determined. It is shown that the doping of YBa YBa$_2$Cu$_3$O$_{7-\delta}$ with cadmium leads to an increase in the coherence length along the c axis by a factor of 3.2. An analysis of the excess conductivity of the Y$_{0.5}$Cd$_{0.5}$Ba$_2$Cu$_3$O$_{7-\delta}$ sample within the framework of the local pair model made it possible to determine the temperature dependences of the pseudogap and its maximum value.