Topological antiferromagnetic spin-density-wave phase in an extended Kondo lattice model

Abstract

By using an extended mean-field theory, we study the phase diagram of the topological Kondo lattice model on the honeycomb lattice at half-filling in which the conduction electrons are described by the Haldane model. Besides the well-defined Kondo insulator and normal antiferromagnetic spin-density-wave (N-SDW) state, it is found that a nontrivial topological antiferromagnetic SDW state (T-SDW) with a quantized Hall conductance is possible if the quasiparticle gap is dominated by the next-nearest-neighbor hopping rather than the antiferromagnetic order. By analyzing the low-energy effective Chern-Simon action and the corresponding chiral edge state, the T-SDW could be considered as a quantum anomalous Hall insulator with antiferromagnetic long-range order. This state is apparently beyond Landau-Ginzburg paradigm, which can be attributed to the interplay of quantum anomalous Hall effect and the subtle antiferromagnetic order in the Kondo-lattice-like model. While the transition between the SDW states and the Kondo insulator is found to be conventional (a first order transition), the transition between the N- and T-SDWs is, however, a topological quantum phase transition. Interestingly, such topological quantum phase transition can be described by Dirac fermions coupled to a U (1)Chern-Simon gauge field, which resembles the critical theory between bosonic integer quantum Hall phases and superfluid phase and also indicates that such a topological quantum phase transition may fall into the 3D-XY universal class. It is expected that the present work may shed light on the interplay between conduction electrons and the densely localized spins on the honeycomb lattice.

11pages,3figures. Fluctuation effect is included and critical theory for the topological quantum phase transition is also derived

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