The strong coupling Kondo lattice model as a Fermi gas

TL;DR

This paper introduces an exact transformation that maps the strongly interacting half-filled Kondo lattice model to a dilute Fermi gas of quasiparticles, enabling conventional analysis of its properties.

Contribution

The authors derive an exact transformation that maps the strong coupling Kondo lattice model to a weakly interacting quasiparticle gas, facilitating analysis of its strongly correlated behavior.

Findings

Exact mapping to a dilute quasiparticle gas

Quasiparticle vacuum as a singlet Mott insulator

Spectral weight sum rules are exactly obeyed

Abstract

The strong coupling half-filled Kondo lattice model is an important example of a strongly interacting dense Fermi system for which conventional Fermi gas analysis has thus far failed. We remedy this by deriving an exact transformation that maps the model to a dilute gas of weakly interacting electron and hole quasiparticles that can then be analyzed by conventional dilute Fermi gas methods. The quasiparticle vacuum is a singlet Mott insulator for which the quasiparticle dynamics are simple. Since the transformation is exact, the electron spectral weight sum rules are obeyed exactly. Subtleties in understanding the behavior of electrons in the singlet Mott insulator can be reduced to a fairly complicated but precise relation between quasiparticles and bare electrons. The theory of free quasiparticles can be interpreted as an exactly solvable model for a singlet Mott insulator, providing an exact model in which to explore the strong coupling regime of a singlet Kondo insulator.