O17 NMR Study of Undoped and Lightly Hole Doped CuO2 Planes

Using 17O NMR, we probed the short wavelength excitations in the CuO2 planes of insulating and weakly metallic high Tc cuprates. We measured the spin wave damping for an S=1/2 2D quantum Heisenberg antiferromagnet for the first time. The results establish the nearly free behavior (asymptotic freedom) of the high energy spin waves, even without long range magnetic order. Light hole doping dramatically enhances the low energy excitation spectrum below 300 K.