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

Abstract

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<T<T′≈105(2)K, far below T∗. This is confirmed by the magnetic field dependence of the microwave absorption. Hence, our results support the distinction between the physical processes of pseudogap and the superconducting ordering.