Dynamics of the local moment induced by nonmagnetic defects in cuprates

We present a study of the spin dynamics of magnetic defects induced by Li s ubstitution of the plane Cu in the normal state of YBa2Cu3O6+x. The fluctua tions of the coupled Cu magnetic moments in the vicinity of Li are probed b y near-neighbor Y-89 and Li-7 NMR spin lattice relaxation. The data indicat e that the magnetic perturbation fluctuates as a single entity with a cell- elation time tau which scales with the local static susceptibility. This be havior is reminiscent of the low T Kondo state of magnetic impurities in co nventional metals. Surprisingly it extends well above the "Kondo" temperatu re fur the underdoped pseudogapped case.