Essence of Pseudogap and Oscillation in High-Temperature Cuprate Superconductor Junction of Pseudogap State

This paper gives methods to calculate the pairing temperatureT^*, at which a pseudogap is opened, and the superconductingtemperature T_c, at which superconductivity appears, in thehigh-T_c cuprates, and demonstrates directly that at T_c<T<T^*the pseudogap is the gap of Cooper pair without long-range phasecoherence, and at T<T_c there is long-range phase coherence betweenCooper pairs. Based on the above clear physical picture on thepseudogap state and our mechanism for the ac Josephson effect,this paper proposes that there should be a novel oscillatory currentin P-I-P junction, induced by a constant bias on the junction.Here, P represents the high-T_c curates in the pseudogap state,where Cooper pairs do not have long-range phase coherence, and Irepresents the thin insulating barrier. This paper conjectures thatthere is a possible high-temperature superconductivity in the heavilyunderdoped high-T_c cuprates.