Superconducting fluctuations and the pseudogap in the slightly overdoped high-T-c superconductor TlSr2CaCu2O6.8: High magnetic field NMR studies

From measurements of the Cu-63 Knight shift (K) and the nuclear spin-lattic e relaxation rate (1/T-l) under magnetic fields from zero up to 28 T in the slightly overdoped high-T-c. superconductor TlSr2CaCu2O6.8 (T-c = 68 K), w e find that the pseudogap behavior, i.e., the reductions of 1/TlT and K abo ve T-c from the values expected from the normal state at high T, is strongl y field dependent and follows a scaling relation. We show that this scaling is consistent with the effects of the Cooper pair density fluctuations. Th e present finding contrasts sharply with the pseudogap property reported pr eviously in the underdoped regime where no field effect was seen up to 23.2 T. The implications are discussed.