Partial and macroscopic phase coherences in an underdoped Bi₂Sr₂CaCu₂O_8+δ thin film

A combined study using the time-resolved pump-probe technique and the time domain terahertz transmission spectroscopy has been carried out to investigate the normal-state anomalies in underdoped Bi₂Sr₂CaCu₂O_8+δ. It was observed that a superconducting gap and a pseudogap coexist in the superconducting state. The pseudogap locally evolves below T* ≃ 210 K simultaneously with the appearance of partial phase coherence with a short lifetime less than 1 ps. With decreasing temperature, the domains with a pseudogap developed and saturated at T_S ∼ 95 K, and the frequency-dependent superconductivity fluctuation appeared as cooperative phenomena among the partial phase-coherent domains. These experimental data show that the development of the partial coherent local domains with a pseudogap has an important role to switch from the partial to the macroscopic phase-coherent state.