Fluctuations in the microwave conductivity of YBa2Cu3O7-delta single crystals in zero dc magnetic field

We present a quantitative analysis of finite frequency fluctuation conductivity above and below T-c in cuprate superconductors in zero de magnetic field. In a YBa2Cu3O7-delta crystal showing a linear in temperature increase of the penetration depth at low temperatures, we find that two-dimensional (2D) finite frequency Gaussian conductivity fluctuations above T-c cross over into a slower divergence of the conductivity as T-c is approached from above. We find that the critical regime above T-c is less than about 0.6 K wide. At and below T-c, 3D fluctuations dominate the conductivity, with evidence of 3D XY critical scaling of the imaginary part of the conductivity down to 5 K below T-c.