Pseudogap and superconducting fluctuations in Bi2Sr2CaCu2O8+y probed by

We report temperature dependence of the Gaussian component of spin-echo decay rate (1/T2G) in single crystals Bi2Sr2CaCu2O8+y(Bi2212). We found that 1/T2G starts to decrease at a certain temperature, , which is higher than Tc and lower than the pseudogap temperature, T∗, suggesting the formation of local Cooper pairing without global phase coherency. Based on our NMR results, we develop the phase diagram in the Bi2212 system which includes three crossover temperatures, and .