Microwave measurements of the in-plane and c -axis conductivity in HgBa2 CuO4+δ: Discriminating between superconducting fluctuations and pseudogap effects

An approach to microwave measurements is used in order to determine both, the in-plane and out-of-plane conductivity of the high- Tc superconductor HgBa2 CuO4+δ near optimal doping. Unlike the ab -plane conductivity, the c -axis conductivity is highly sensitive to superconducting fluctuations. From a single c -axis data set, we can clearly discern the opening of the pseudogap at T =185 (15) K, the appearance of the superconducting fluctuations at a much lower temperature T′ =105 (2) K, and the full transition to the superconducting state at the critical temperature Tc =94.3 K. Thus, with the present high sensitivity, we establish that the extent of the superconducting fluctuations is only about 10 K above Tc.