NUCLEAR-MAGNETIC-RESONANCE OF PLANE CU IN PARAMAGNETIC YBA2CU3O6

The first observation of the NMR of plane Cu in the paramagnetic state of YBa2Cu3O6 is reported. The NQR frequency and the anisotropies of the magnetic shift tensor and of the spin-lattice and spin-spin relaxation times have been measured. Evidence for a strong indirect spin-spin coupling of plane Cu nuclei mediated by the exchange coupled electrons has been found. The spin-lattice relaxation rate anisotropy is close to the value expected for purely dipolar interaction between the nuclear spin and the electronic spin of the Cu(2) 3d(x2-y2) hole. An "extra" anistropy observed in the superconductor YBa2Cu3O7 seems to arise from carriers and should be therefore dependent on their concentration.