Phase diagram of the Hubbard-Kondo lattice model from variational cluster approximation

TL;DR

This study uses variational cluster approximation to map the phase diagram of the two-dimensional Hubbard-Kondo lattice model, revealing the dominance of antiferromagnetic, ferrimagnetic, and Kondo singlet phases depending on electron filling and interaction strengths.

Contribution

It provides a detailed phase diagram of the Hubbard-Kondo lattice model, highlighting the competition between magnetic ordering and Kondo singlet formation using an advanced variational method.

Findings

Antiferromagnetic phase dominates at half-filling for small to moderate interactions.

Ferrimagnetic phase appears away from half-filling before transitioning to Kondo singlet.

Phase transitions depend on electron filling and interaction parameters.

Abstract

The interplay between the Kondo effect and magnetic ordering driven by the Ruderman-Kittel-Kasuya-Yosida interaction is studied within the two-dimensional Hubbard-Kondo lattice model. In addition to the antiferromagnetic exchange interaction, $J_\perp$, between the localized and the conduction electrons, this model also contains the local repulsion, $U$, between the conduction electrons. We use variational cluster approximation to investigate the competition between the antiferromagnetic phase, the Kondo singlet phase, and a ferrimagnetic phase on square lattice. At half-filling, the N\'eel antiferromagnetic phase dominates from small to moderate $J_\perp$ and $UJ_\perp$, and the Kondo singlet elsewhere. Sufficiently away from half-filling, the antiferromagnetic phase first gives way to a ferrimagnetic phase (in which the localized spins order ferromagnetically, and the conduction electrons do likewise, but the two mutually align antiferromagnetically), and then to the Kondo singlet phase.