Dynamics of the Local Moment Induced by Nonmagnetic Defects in Cuprates

TL;DR

This paper investigates how nonmagnetic Li defects induce local magnetic moments in cuprates, revealing a Kondo-like fluctuation behavior that persists above the expected temperature range.

Contribution

It demonstrates that Li-induced magnetic fluctuations in cuprates behave like a Kondo state, extending beyond the traditional temperature limits, providing new insights into impurity effects in high-Tc superconductors.

Findings

Magnetic perturbations fluctuate as a single entity with a correlation time.

Fluctuation behavior scales with local static susceptibility.

Kondo-like behavior persists above the Kondo temperature.

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 $\tau$ 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.