Eur. Phys. J. B (2013) 86: 195
https://doi.org/10.1140/epjb/e2013-31091-7

Regular Article

Half-filled Kondo lattice on the honeycomb lattice

¹ Center for Interdisciplinary Studies Key Laboratory for Magnetism and Magnetic Materials of the MoE, Lanzhou University, Lanzhou 730000, P.R. China
² Institute of Theoretical Physics, Lanzhou University, Lanzhou 730000, P.R. China
³ Beijing Computational Science Research Center, Beijing 100084, P.R. China

^a e-mail: zhongy05@hotmail.com

Received: 5 December 2012
Received in final form: 27 February 2013
Published online: 29 April 2013

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 study on the interplay between conduction electrons and the densely localized spins on the honeycomb lattice.