The Kondo screening cloud: what it is and how to observe it

TL;DR

This paper reviews the Kondo effect's long length scale, the Kondo screening cloud, discussing how it manifests as a crossover scale and proposing experiments to observe this elusive phenomenon.

Contribution

It provides a comprehensive analysis of the Kondo screening cloud and suggests experimental approaches to detect its long characteristic length scale.

Findings

Kondo length scale estimated to be 0.1 to 1 microns

Proposes experimental methods to observe the Kondo cloud

Discusses crossover behavior related to the Kondo length

Abstract

The Kondo effect involves the formation of a spin singlet by a magnetic impurity and conduction electrons. It is characterized by a low temperature scale, the Kondo temperature, $T_K$, and an associated long length scale, $\xi_K = \hbar v_F/(k_BT_K)$ where $v_F$ is the Fermi velocity. This Kondo length is often estimated theoretically to be in the range of .1 to 1 microns but such a long characteristic length scale has never been observed experimentally. In this review, I will examine how $\xi_K$ appears as a crossover scale when one probes either the dependence of physical quantities an distance from the impurity or when the impurity is embedded in a finite size structure and discuss possible experiments that might finally observe this elusive length scale.