Unifying Kondo coherence and antiferromagnetic ordering in the honeycomb lattice

Abstract

In this paper, we describe a mechanism by which the destruction of the Kondo coherence at the same time gives rise to antiferromagnetic ordering. This picture is in contrast to the Doniach picture of the competition of Kondo coherence and antiferromagentic ordering. Our study is done in the honeycomb lattice at half-filling, where Kondo coherence gives rise to a Kondo insulator. We go beyond mean-field (large $N$) formulation of Kondo coherence in Kondo lattices and consider excitations we call Kondo vortices. A Kondo vortex is a configuration where at its core the Kondo amplitude vanishes while far away from the core it retains the uniform Kondo amplitude. A Kondo vortex in our model brings four zero modes to the chemical potential. The zero modes play a crucial role as they allow us to construct spin-1 operators. We further study the transformation of these spin-1 Kondo vortex operators under various symmetry transformations of the Kondo Hamiltonian and find a class of operators that transform like an antiferromagnetic order parameter. This gives a novel picture of how one can create antiferromagnetic ordering by proliferating Kondo vortices inside a Kondo coherent phase. We finish by studying the universality class of this Kondo vortex mediated antiferromagnetic transition and conclude that it is in the $O(3)$ universality class.