NMR Investigation of Low-Energy Excitations in YBa2Cu3O6+x Single Crystals

17O and 63Cu NMR results obtained in three single crystals of YBa2Cu3O6+x, 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 — overdoped for x > 0.94, underdoped for x < 0.94. In the overdoped regime a Fermi liquid description seems to be correct, while in the underdoped regime a pseudo-gap in the magnetic excitations opens well above Tc, supporting the phase diagram based on the spin-charge separation. We also show that both neutron inelastic scattering results and Cu(2) and 0(2,3) NSLRR results can be explained using the same χ″(q, ω).