Valley-Polarized Quantum Anomalous Hall Effect in Silicene

We find theoretically a new quantum state of matter-the valley-polarized quantum anomalous Hall state in silicene. In the presence of Rashba spin-orbit coupling and an exchange field, silicene hosts a quantum anomalous Hall state with Chern number C = 2. We show that through tuning the Rashba spin-orbit coupling, a topological phase transition results in a valley-polarized quantum anomalous Hall state, i.e., a quantum state that exhibits the electronic properties of both the quantum valley Hall state (valley Chern number C-v = 3) and quantum anomalous Hall state with C = -1. This finding provides a platform for designing dissipationless valleytronics in a more robust manner.