  It is shown that topological insulating phases driven by interactions can be
realized without the need for spin-orbit coupling or large intersite
interaction in a two-dimensional system of spin-1/2 fermions with a single pair
of parabolically touching bands. Using a weak-coupling, Wilsonian
renormalization group procedure, we show that a quantum anomalous Hall phase is
realized for Hubbard interaction, while a quantum spin Hall phase is favored
for longer-ranged interactions.
