NMR Experimental Test for the Existence of the Kondo Resonance

Abstract

A major part of the information about the behavior of impurities in a metal is contained in the conduction electron scattering on the impurities described, e.g., by a t-matrix. Theories are more or less primarily directly concerned with the t-matrix; experimentally, however, this quantity is not directly accessible. Investigation of the transport properties (mainly resistivity) is the usual way to obtain information about impurity scattering, in which case we are actually concerned with some integrals containing the t-matrix and confined to a narrow energy range around the Fermi energy, characterized by a width scaling with kT. As we will show, the charge density oscillation (Friedel oscillation¹) around the impurity is also generally related to some integral containing the t-matrix and having its most important contributions from the vicinity of the Fermi energy. This integral is different from those involved in transport phenomena; in particular, it is essentially temperature independent (except for a possible temperature dependence of the t-matrix itself). We will find that the additional information one can obtain from the investigation of the charge density oscillation, combined with the readily available data about the effect of the impurity on the bulk transport properties, yields a powerful tool to study the energy dependence of the t-matrix. It is particularly important to note that this method works at a given temperature; it therefore offers the new possibility of direct separation of the energy and the temperature dependence of the scattering, which is not present in the usual scheme based on transport property studies.

On leave from the Central Research Institude for Physics, Budapest, Hungary.