| The Hubbard model is one of the most studied microscopic models in condensed matter physics. Generically, one expects at half filling a metallic phase for large kinetics while a long-range ordered Mott insulator is present for large interactions. A direct transition between the metal and the long-range ordered Mott insulator was considered to be the standard case for a long time. But in recent years there are more and more evidences that there is the possibility of exotic and insulating intermediate phases. It is therefore an obviously relevant question what kind of effective low-energy theory describes such Mott phases and how to derive them. In this talk we discuss these issues for the Mott phase of the Hubbard model on the triangular and on the honeycomb lattice. To this end a novel scheme to derive effective models non-perturbatively is introduced. |
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