Pseudogap behavior in single crystals of Bi2Sr2CaCu2O8+δ

In under- and optimally doped Bi2Sr2CaCu2O8 (Bi2212), we found a characteristic temperature T-K(*);s below which the spin part of Knight shift K-s starts to decrease steeply and extrapolates to zero at T > 0. TK is in good agreement with the temperatures at which the pseudogap starts to open in the quasiparticle density of states (DOS) at the Fermi level, and T* at which 1/T1T has a broad peak. We propose that the spin-gap behavior observed in NMR measurements has the same origin as the pseudogap in the quasiparticle DOS. (C) 1999 Elsevier Science B.V. All rights reserved.