To the two-dimensional character of superconducting transition for undoped HTS

Abstract

The dimensional 3D®2D crossover is studied for quisi-two-dimensional HTS in a superconducting state. Using the general laws of superconducting state for 2D and 3D systems a universal dependence of the relation between penetration lengths of magnetic field along axis ĉ , l²(0)/l²(T/T_c), is obtained. It is shown that this dependence leads to the known universal relation between the temperature of super-conducting transition, T_c, and the value of l^-2(0) for quisi-two-dimensional HTS. This permits the temperature of dimensional crossover, T_cr < T_c, to be defined as the boundary of two-dimensional region, where the measured values of l²(0)/l²(T/T_c) at T > T_cr begin to depart from the universal relation obtained. It is shown that the region of three-dimensional superconducting fluctuations is finite evidencing the two-dimensional character of super-conducting transition for quisi-two-dimensional HTS.