  We find a state characterized by a spontaneous loop-spin current and a
single-particle gap in the Hubbard model within the variational cluster
approach. This state exists for arbitrarily small interaction in a half-filled
honeycomb lattice. Moreover, from the calculations of the topological
invariants for the interacting system, it is shown that this gapped state has
nontrivial topological characters; this state is the topological Mott
insulating state. This result implies the ubiquity of topological Mott
insulating phases.
