Metal-insulator transition in the one-dimensional Kondo lattice model

TL;DR

This paper investigates the one-dimensional Kondo lattice model using non-Abelian bosonization, revealing a Kondo insulator at half-filling and a heavy-fermion state away from half-filling, with implications for magnetic instability.

Contribution

It introduces a detailed analysis of the phase diagram of the 1D Kondo lattice model, including the SDG state and the normal heavy-fermion state, using non-Abelian bosonization.

Findings

Kondo insulator with a linear gap at half-filling

Presence of a Spin Density Glass state at half-filling

Heavy-fermion state with a long-range antiferromagnetic polarization away from half-filling

Abstract

We study the usual one-dimensional Kondo lattice model (1D KLM) using the non-Abelian bosonization formalism. At half-filling, we obtain a Kondo insulator with a gap in both charge and spin excitations which varies quite linearly with the Kondo exchange $J_K$. It consists of a Spin Density Glass state, or a $q=\pi$ spin density wave weakly pinned by a nearly antiferromagnetically ordered spin array. We will analyze the stability of the SDG state in presence of randomness. We will compare these results with those obtained in the one-dimensional Heisenberg-Kondo lattice model (1D HKLM) where the spins are coupled through a large Heisenberg exchange. Away from half-filling, the system is metallic and yields a very small spin gap which is equal to the one-impurity Kondo gap $T_k^{(imp)}$. Unlike the one-impurity Kondo model, we will show why this Kondo phase cannot rule the fixed point of the 1D KLM, away from half-filling. We will rather obtain a normal heavy-fermion state controlled by the energy scale $T_{coh}\sim (T_k^{(imp)})^2/t$ (t is the hopping term) with a quite long-range antiferromagnetic polarization. It is important to notice that both the SDG state and the normal heavy-fermion state are susceptible to occur near a magnetic instability.