Distinctive behavior of superconducting fluctuations and pseudogap in nearly optimally doped single crystal of HgBa2CuO4+δ

We have applied an unconventional microwave measurement approach to a nearly optimally doped HgBa2CuO4+δ single crystal. The sample geometry assured the total lateral penetration of microwaves due to weak c-axis screening currents. With this configuration, one can achieve excellent sensitivity to small changes in conductivity. The data show that the pseudogap opens at T∗=185(15)K, which is almost twice the superconducting critical temperature Tc=94.3K. In contrast, the superconducting fluctuation regime is clearly confined to a narrow temperature range Tc