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 substitution of the plane Cu in the normal state of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$. The fluctuations of the coupled Cu magnetic moments in the vicinity of Li are probed by near-neighbor ${}^{89}\mathrm{Y}$ and ${}^7\mathrm{Li}$ NMR spin lattice relaxation. The data indicate that the magnetic perturbation fluctuates as a single entity with a correlation time $\tau$ which scales with the local static susceptibility. This behavior is reminiscent of the low $T$ Kondo state of magnetic impurities in conventional metals. Surprisingly it extends well above the “Kondo” temperature for the underdoped pseudogapped case.