REAL-SPACE PAIR MODEL PREDICTIONS FOR THE NMR BEHAVIOR IN HIGH-TC CUPRATES

A model for real-space singlet pairs, hopping on the quasi 2D antiferr omagnetic background of localized spins is further analysed. It is sho wn that lattice vibrations (if any), which break the symmetry of the i n-plane oxygen position with respect to the nearest neighboring copper sites, may strongly influence both the magnitude and the temperature dependence of the O-17 NMR relaxation rate. For the Y site a situation is analogous, although the different modes may contribute to the effe ct. A relation of the results obtained to the Millis-Monien-Pines anal ysis is discussed. The validity of the mean-field random phase approxi mation for the description of the 2D antiferromagnet used previously i s analysed. It is shown that the 2D fluctuations of the phase of the ( bond) mean field parameter lead to the power-law decay with the distan ce of the corresponding correlation function (which remains finite in the mean field approximation). The spectrum of the phase fluctuations is found to be propagative in the one-loop approximation. An interacti on of the real-space singlet pairs with the long-wavelength phase fluc tuations is discussed.