Dynamics of the Local Moment Induced by Nonmagnetic Defects in Cuprates

Abstract

We present a study of the spin dynamics of magnetic defects induced by Li substitution of the plane Cu in the normal state of YBa${}_2$Cu${}_3$O${}_{6+x}$. The fluctuations of the coupled Cu magnetic moments in the vicinity of Li are probed by near-neighbour ${}^{89}$Y {\it and} ${}^7$Li NMR spin lattice relaxation. The data indicates that the magnetic perturbation fluctuates as a single entity with a correlation time $\ddot{I}„$ which scales with the local static susceptibility. This behaviour 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.

4 pages, 5 figures (same), major modifications to text, accepted in PRL