Topological insulators in three dimensions from spontaneous symmetry breaking

We study three-dimensional systems where strong repulsion leads to an insulating state via spontaneously generated spin-orbit interactions. We discuss a microscopic model where the resulting state is topological. Such topological “Mott” insulators differ from their band-insulator counterparts in that they possess an additional order parameter, a rotation matrix, which describes the spontaneous breaking of spin-rotation symmetry. We show that line defects of this order are associated with protected one-dimensional modes in the strong topological Mott insulator that provides a bulk characterization of this phase. Possible physical realizations in cold-atom systems are discussed.