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Microwave measurements of the in-plane and c-axis conductivity in HgBa$_2$CuO$_{; ; 4+\delta}; ; $: 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-$T_c$ superconductor HgBa$_2$CuO$_{; ; ; 4+\delta}; ; ; $ 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 $T_c=94.3 K$. Thus, with the present high sensitivity, we establish that the extent of the superconductiong fluctuations is only about 10 K above T_c.

cuprate superconductors; microwaves; pseudogap; fluctuations

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