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The Hubbard model is one of the most studied microscopic models in condensed matter physics. It describes on a very simple level the interplay between the kinetics and the Coulomb interaction of electrons in solid state systems. Generically, one expects at half filling a metallic phase for large kinetics while a Mott insulator is present for large interactions. In most cases the Mott phase shows additionally long-range spin order, since the Hubbard model can be mapped to a Heisenberg model in the strong-coupling limit. 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 especially on frustrated lattices there is the possibility of exotic and insulating intermediate phases without long range order. It is therefore an obviously relevant question what kind of effective low-energy theory describes such Mott phases and how to derive them. This is particular complicated when the spin liquid is located close to the metal-insulator transition as for the recently discovered spin liquid of the Hubbard model on the honeycomb lattice. In this talk we discuss these issues for the Mott phase of the Hubbard model on the triangular and on the honeycomb lattice.

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Kai P. Schmidt, TU Dortmund
Seminarraum Theoretische Physik
Contact: not specified