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

An attempt is made to interpret the experiments in which the superconducting transition temperature in underdoped HTSC was found to depend on the direction of the current passing through the sample. It is suggested that one (higher) temperature approximately corresponds to the point TBKT of the two-dimensional transition, while the other is the temperature Tc corresponding to 3D ordering between layers. For conditions when Tc⩾TBKT (relatively high values of carrier concentration and interlayer coupling), the anisotropy of the superconducting properties becomes negligible and the layered system possesses only one critical temperature.