Strong pairing interaction and pseudogap behavior in underdoped Bi2Sr2CaCu2O8+delta

We report STM/STS and Raman experiments on the Bi2212 superconducting gap i n a doping range from p similar to 0.1 to similar to 0.21. The gap magnitud e 2 Delta(o) at T much less than T-c increases with lowering p even in the underdoped region, as in the p dependence of the onset temperature T* of a pseudogap. T* is in qualitative agreement with the mean-field value of T-c, T-c(MF), Obtained from 2 Delta(o). This result indicates that T* correspon ds to T-c(MF), suggesting convincingly that incoherent pairs are preformed below T*. (C) 1998 Elsevier Science Ltd. All rights reserved.