Ferromagnetism and quantum anomalous Hall effect in one-side-saturated buckled honeycomb lattices

The recently synthesized silicene as well as theoretically discussed germanene are examples of buckled honeycomb structures. The buckled structures allow one to manipulate asymmetry between two underlying sublattices of honeycomb structures. Here by taking germanene as a prototype of buckled honeycomb lattices, we explore magnetism induced by breaking sublattice symmetry through saturating chemical bonds on one-side of the buckled honeycomb lattice. It is shown that when fractions of chemical bonds on one-side are saturated, two narrow bands always exist at half filling. Furthermore, the narrow bands generally support flat band ferromagnetism in the presence of the Hubbard $U$ interaction. The induced magnetization is directly related to the saturation fraction and is thus controllable in magnitude through the saturation fraction. Most importantly, we find that depending on the saturation fraction, the ground state of an one-side saturated germanene may become a quantum anomalous Hall (QAH) insulator characterized by a Chern number that vanishes for larger magnetization. The non-vanishing Chern number for smaller magnetization implies that the associated quantum Hall effect tends to survive at high temperatures. Our findings provide a potential method to engineer buckled honeycomb structures into high-temperature QAH insulators.