On the two-dimensional character of the superconducting transition in underdoped high-temperature superconductors

The 3D --> 2D dimensional crossover in the superconducting state of quasi-t wo-dimensional high-T-c superconductors is investigated. The consistent pat tern of the superconducting state of 2D and 3D systems is used to find a un iversal temperature dependence of the ratio of the squares of the penetrati on depths of a magnetic field directed along the c axis, i.e., lambda (2)(0 )/lambda (2)(T/T-c), from which one can obtain a relation between the super conducting transition temperature T-c and lambda (-2)(0). This yields the t emperature T-cr of the dimensional crossover as the boundary of the region of "two-dimensionality" of the superconducting state, where for T >T-cr the results of measurements of the penetration depth begin to deviate from the universal dependence found. It is shown that the size of the region of thr ee-dimensional superconducting fluctuations can be determined from measurem ents of lambda (T/T-c) and the resistance along the c axis and turns out to be finite, attesting to the 2D character of the superconducting transition in quasi-2D HTSCs. (C) 2001 American Institute of Physics.