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 antiferromagnetic background of localized spins is further analysed. It is shown that lattice vibrations (if any), which break the symmetry of the in-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 effect. A relation of the results obtained to the Millis-Monien-Pines analysis is discussed. The validity of the mean-field random phase approximation for the description of the 2D antiferromagnet used previously is 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 distance 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 interaction of the real-space singlet pairs with the long-wavelength phase fluctuations is discussed.