Half-filled Kondo lattice on the honeycomb lattice

TL;DR

This study investigates the phase diagram of the half-filled Kondo lattice model on the honeycomb lattice, revealing a coexistence region of Kondo screening and antiferromagnetic order due to the linear density of states.

Contribution

It introduces an extended mean-field approach that captures the coexistence of Kondo screening and magnetic order, highlighting the effects of the honeycomb lattice's linear density of states.

Findings

Existence of a coexistence region with Kondo screening and antiferromagnetic order.

A minimum Kondo coupling strength is required for the Kondo insulator phase.

The antiferromagnetic transition falls into the O(3) universality class.

Abstract

The unique linear density of state around the Dirac points for the honeycomb lattice brings much novel features in strongly correlated models. Here we study the ground-state phase diagram of the Kondo lattice model on the honeycomb lattice at half-filling by using an extended mean-field theory. By treating magnetic interaction and Kondo screening on an equal footing, it is found that besides a trivial discontinuous first-order quantum phase transition between well-defined Kondo insulator and antiferromagnetic insulating state, there can exist a wide coexistence region with both Kondo screening and antiferromagnetic orders in the intermediate coupling regime. In addition, the stability of Kondo insulator requires a minimum strength of the Kondo coupling. These features are attributed to the linear density of state, which are absent in the square lattice. Furthermore, fluctuation effect beyond the mean-field decoupling is analyzed and the corresponding antiferromagnetic spin-density-wave transition falls into the O(3) universal class. Comparatively, we also discuss the Kondo necklace and the Kane-Mele-Kondo (KMK) lattice models on the same lattice. Interestingly, it is found that the topological insulating state is unstable to the usual antiferromagnetic ordered states at half-filling for the KMK model. The present work may be helpful for further studies on the interplay between conduction electrons and the densely localized spins on the honeycomb lattice.