The Screening Cloud in the k-Channel Kondo Model: Perturbative and Large-k Results

TL;DR

This paper investigates the large Kondo screening cloud in the k-channel Kondo model using perturbation theory and large-k analysis, revealing detailed spatial and temperature-dependent properties consistent with experimental observations.

Contribution

It provides a comprehensive analysis of the screening cloud profile and Green's functions in the k-channel Kondo model, including large-k limit results and their physical implications.

Findings

Large Kondo screening cloud exists in the k-channel model.

Green's functions show oscillations at twice the Fermi wave-vector.

Susceptibility mainly from impurity-impurity interactions, with conduction electrons suppressed.

Abstract

We demonstrate the existence of a large Kondo screening cloud in the k-channel Kondo model using both renormalization group improved perturbation theory and the large-k limit. We study position (r) dependent spin Green's functions in both static and equal time cases. The equal-time Green's function provides a natural definition of the screening cloud profile, in which the large Kondo scale appears. At large distances it consists of both a slowly varying piece and a piece which oscillates at twice the Fermi wave-vector. This function is calculated at all r in the large-k limit. Static Green's functions (Knight shift or susceptibility) consist only of a term oscillating at 2kF, and appear to factorize into a function of r times a function of T for rT << vF, in agreement with NMR experiments. Most of the integrated susceptibility comes from the impurity-impurity part with conduction electron contributions suppressed by powers of the bare Kondo coupling. The single-channel and overscreened multi-channel cases are rather similar although anomalous power-laws occur in the latter case at large r and low T due to irrelevant operator corrections.