  In the presence of extrinsic Rashba spin-orbit coupling, we find that
silicene can host a new quantum anomalous Hall state with spin- and
valley-polarized edge states, which can be effectively controlled by the
exchange field and electric field. In this new state, the pair of nontrivial
edge states reside in one specific valley and have a strong but opposite spin
polarization. A distinctive feature of this new state is that both of the spin
and valley index of the edge states can be switched by reversing the electric
field. We also present a microscopic mechanism for the origination of the new
state. Our findings provide an efficient way to control the topologically
protected spin- and valley-polarized edge states, which is crucial for
spintronics and valleytronics.
