EVIDENCE FOR ANGSTROM THICKNESS OF HTSC I SOLATED SUPERCONDUCTING LAYERS

The effective thickness of YBa2Cu3Ox superconducting layers is evaluat ed. The abnormally large difference between the mean-field critical te mperature and the temperature of Berezinskii-Kocterlitz-Thouless (BKT) transition in orle-unit-cell films, Y/Pr superlattices and polycrysta l samples with destroyed CuO2 planes, is explained. The dynamics of th e BKT temperature with varying the number of the layered YBa2Cu3Ox uni t cells is described. Art expression that relates the BKT transition t emperature to sample resistance per square area and is appropriate For HTSC is derived.