Stability of spontaneous quantum Hall state in the Triangular Kondo-lattice model

We study the behavior of the quarter-filled Kondo lattice model on a triangular lattice by combining a zero-temperature variational approach and finite-temperature Monte-Carlo simulations. For intermediate coupling between itinerant electrons and classical moments ${\bf S}_j$, we find a thermodynamic phase transition into an exotic spin ordering with uniform scalar spin chirality and $\langle {\bf S}_j \rangle=0$. The state exhibits spontaneous quantum Hall effect. We also study how its properties are affected by the application of an external magnetic field.