Impurity Entanglement Entropy and the Kondo Screening Cloud

TL;DR

This paper investigates how the entanglement entropy around a magnetic impurity in a metal scales with distance, revealing universal behavior linked to the Kondo screening cloud using numerical and analytical methods.

Contribution

It introduces a universal scaling function for impurity entanglement entropy in the Kondo problem, derived via DMRG and Fermi liquid theory.

Findings

Impurity entanglement entropy is a universal function of r/xi_K and r/R.

The scaling function is computed analytically in the regime xi_K << r.

Results confirm the universal nature of entanglement in Kondo systems.

Abstract

The screening of an impurity spin by conduction electrons is associated with the formation of a large Kondo screening cloud, of size xi_K. We study the quantum entanglement between a region of size r surrounding the impurity and the rest of the sample, (of total size R) using Density Matrix Renormalization Group and analytic methods. The corresponding "impurity entanglement entropy", S_{imp}, is shown to be a universal scaling function of r/xi_K and r/R. We calculate this universal function using Fermi liquid theory in the regime xi_K << r.