NMR INVESTIGATION OF SINGLE-CRYSTAL YBA2CU3O6+X FROM THE UNDERDOPED TO THE OVERDOPED REGIME

O-17 and Cu-63 NMR results obtained in three single crystals of YBa2Cu3O6+x, YBa1.92Sr0.08Cu3O7 (T(c)=89 K) which is overdoped, and YBa1.93Sr0.07Cu3O6.92 (T(c)=91 K) and YBa2Cu3O6.52 (T(c)=59 K) which are underdoped, show that the static spin susceptibility and (T1T)-1 for Cu(2) and O(2,3) have completely different temperature dependence according to the regime and irrespective of T(c). The principal characteristic of the underdoped regime is the opening of a pseudogap in the magnetic excitations well above T(c), supporting the phase diagram based on the spin-charge separation. The contribution of the antiferromagnetic fluctuations at the O(2,3) sites have been observed in YBa1.92Sr0.08Cu3O7, in good agreement with the inelastic-neutron-scattering results.