Yin Zhong, Ke Liu, Yu-Feng Wang, Yong-Qiang Wang, Hong-Gang Luo
The ground-state phase diagram of the Kondo lattice model on the honeycomb lattice at half-filling is carefully studied 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 coexistent region with both Kondo screening and antiferromagnetic orders in the intermediate coupling regime. The appearance of such wide coexistence region is attributed to the unique linear density of state on the honeycomb lattice at half-filling in contrast to the case of square lattice. It is expected such a coexistence region could be realized by experiments of ultra-cold atoms on the honeycomb optical lattices and may be found by quantum Monte Carlo simulation in future since it is free of the `minus sign'. Additionally, the stability of Kondo insulator to the trivial decoupled state requires a minimum strength of the Kondo coupling, which is also the result of the magic linear density of state. We hope the present work may be helpful for further studies on the interplay between conduction electrons and the densely localized spins for the honeycomb lattice.
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http://arxiv.org/abs/1208.1332
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