O-17 NMR EVIDENCE FOR A PSEUDOGAP IN THE MONOLAYER HGBA2CUO4+DELTA

Measurements of the spin shift K-17(s) have been performed for the O-1 7 NMR line in the monolayer cuprate HgBa2CuO4+delta, and yield the spi n susceptibility chi(s)(T) of the CuO2 planes. In the underdoped regim e, chi(s) is found to extrapolate to zero at T greater than or equal t o 0. This indicates that a pseudogap opens at T > T-c, as in YBa2Cu3O 6.6. Therefore, the pseudogap features cannot be explained in terms of a magnetic coupling between CuO2 planes in bilayer systems. In the ov erdoped regime, chi(s)(T) obeys a Pauli-like law, as found in the over doped Ti2Ba2CuO6. Comparing the different monolayer systems, we sugges t some correlation between T-c and distortion effects in the planes, a s monitored by the O-17 NMR linewidth.