Cu nuclear magnetic resonance of aligned single crystals of YBa2Cu3O7- delta

Contrasting Phenomenology of NMR Shifts in Cuprate Superconductors

Nuclear magnetic resonance (NMR) shifts, if stripped of their uncertainties, must hold key information about the electronic fluid in the cuprates. The early shift interpretation that favored a single-fluid scenario will be reviewed, as well as recent experiments that reported its failure. Thereafter, based on literature shift data for planar Cu, a contrasting shift phenomenology for cuprate superconductors is developed, which is very different from the early view while being in agreement with all published data. For example, it will be shown that the hyperfine scenario used up to now is inadequate as a large isotropic shift component is discovered. Furthermore, the changes of the temperature dependences of the shifts above and below the superconducting transitions temperature proceed according to a few rules that were not discussed before. It appears that there can be substantial spin shift at the lowest temperature if the magnetic field is perpendicular to the CuO 2 plane, which points to a localization of spin in the 3 d ( x 2 − y 2 ) orbital. A simple model is presented based on the most fundamental findings. The analysis must have new consequences for theory of the cuprates.

Pure nuclear quadrupole resonance determination of the electric field gradient asymmetry for broad lines

We present an angle dependent nuclear quadrupole resonance (ADNQR) method to determine the electric field gradient asymmetry parameter eta in systems where the resonance line is so broad that the radio frequency field can excite only a portion of the nuclear spins. In this situation, the recently developed spectroscopic methods are not applicable. ADNQR is useful for single crystals and oriented powders, and, for small eta determines eta4. Therefore, it can be used to evaluate fluctuations in eta due to inhomogeneities. We demonstrate the application of ADNQR experimentally to oriented superconducting YBa2Cu3O7 powder.

Nuclear Resonance Properties of YBa 2 Cu 3 O 6+x Superconductors

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) results for copper-63, oxygen-17, and yttrium-89 nuclei in the superconducting composition range of YBa(2)Cu(3)O(6+x) (0.4 </= x </= 1.0) are reviewed and interpreted. Copper NMR shift and susceptibility data, combined with a simple ionic model of local magnetic properties, yield a comprehensive analysis of the normal-state anisotropic susceptibility components and full characterization of the copper spin and orbital hyperfine couplings. Data on the spin-lattice relaxation time of these three nuclear species serve to characterize the highly correlated fermion dynamics in this system. Relaxation data from YBa(2)Cu(3)O(7) (superconducting transition temperature T(c) = 90 K) and oxygen-deficient samples of this material (T(c) approximately 60 K) have been analyzed in terms of meanfield models incorporating short-range antiferromagnetic order, giving a quantitative account of (planar) relaxation for these three nuclei in terms of a single dynamical susceptibility.