On a possible reason behind the anisotropy observed in the superconductingproperties of underdoped cuprates

An attempt is made to interpret the experiments in which the superconductin g transition temperature in underdoped HTSC was found to depend on the dire ction of the current passing through the sample. It is suggested that one ( higher) temperature approximately corresponds to the point T-BKT of the two -dimensional transition, while the other is the temperature T-c correspondi ng to 3D ordering between layers. For conditions when T(c)greater than or e qual to T-BKT (relatively high values of carrier concentration and interlay er coupling), the anisotropy of the superconducting properties becomes negl igible and the layered system possesses only one critical temperature. (C) 1999 American Institute of Physics. [S1063-777X(99)01405-X].