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-17 NMR line in the monolayer cuprate HgBa2CuO4+delta, and yield the spin susceptibility chi(s)(T) of the CuO2 planes. In the underdoped regime, chi(s) is found to extrapolate to zero at T greater than or equal to 0. This indicates that a pseudogap opens at T* > T-c, as in YBa2Cu3O6.6. Therefore, the pseudogap features cannot be explained in terms of a magnetic coupling between CuO2 planes in bilayer systems. In the overdoped regime, chi(s)(T) obeys a Pauli-like law, as found in the overdoped Ti2Ba2CuO6. Comparing the different monolayer systems, we suggest some correlation between T-c and distortion effects in the planes, as monitored by the O-17 NMR linewidth.