Pairing fluctuations in cuprate superconductors: universal properties and trends

The effects of thermal pairing fluctuations on the phase transition in extreme type II superconductors with pronounced uniaxial anisotropy are examined in zero magnetic field. Approaching Tc from below, there is the crossover from quasi-2D to 3D xy-behavior, which belongs to the universality class of an uncharged superfluid. Because phase fluctuations destroy long-range order in strictly 2D systems the fluctuation dominated regime is rather large. Approaching from above, the same crossover occurs, but in this regime the fluctuations in the magnitude of the pairing field dominate. Using the Gaussian approximation we obtain the relevant correlation lengths and show the importance of fluctuations and anisotropy.