Topological states of matter have been the focus of extensive studies

since the discovery of the quantum Hall effect. For band insulators, it has been known that topologically nontrivial states can be stabilized by either external magnetic fields (e.g. the integer quantum Hall effect) or spin-orbit effects (e.g. the recently discovered Z_2 topological insulators). In these band insulators, their topological properties can be fully understood within a non-interacting picture, while interactions are believed to be irrelevant at weak coupling and will destabilize the nontrivial topology at strong coupling. In contrast, we discovered a novel class of topological insulators which are stabilized by interaction effects in the absence of external field or spin-orbit couplings. In particular, I will present in this talk the theoretical studies for certain 2D semi-metals and 3D heavy-fermion Kondo insulators. In both cases, topologically nontrivial insulating states are stabilized at infinitesimal coupling. In the 2D models studied here, we further discovered that, in additional to topological band insulators observed at integer filling and weak coupling, fractional topological states, in strong analogy to the fractional quantum Hall effects, are stabilized in the absence of external magnetic field and/or Landau levels at fractional filings and strong coupling. Possible experimental realizations of these novel states will be discussed in condensed matter systems and ultracold atomic gases.