  Recently, correlated physics such as superconductivity and insulator at
commensurate fractional electron fillings has been discovered in several
different systems with Moire superlattice and narrow electron bands near charge
neutrality. Before we learn more experimental details and the accurate
microscopic models describing the insulators, some general conclusions can
already be made about these systems, simply based on their symmetries and
electron fillings. The insulator in the Moire superlattice is described by an
effective spin-orbital model with approximate higher symmetries than ordinary
spin systems. We demonstrate that both the insulators observed at the 1/2 and
1/4 fillings away from the charge neutrality can be viewed as the boundary of a
three-dimensional bosonic symmetry protected topological phase, and hence have
the 't Hooft anomaly once the spatial symmetries are viewed as internal
symmetries.
