14.11.2006, 16:00 Jungiusstr. 9, Seminarraum 3  SFB 668  Seminar Stellan Östlund (University Göteborg, Sweden): Partial bosonization and nonlinear canonical Transformations applied in the study of doped Mott insulatorsWe show that canonical transformations that are nonlinear in electron operators are not only possible but are in fact necessary to exactly map a Mott insulator to a Fermi vacuum. In the case where the Mott insulator has odd valence, the transformation maps Fermionic electron operators to a single chargelike Fermi operator coupled to generalized "quasi" spin operators. The quasispin operators commute at different points in space and physical spin and charge are represented by composite operators. We show that the canonical transformation that maps the Mott insulator to a Fermi vacuum cannot commute with charge, so if this type of transformation properly captures the physics of the Mott insulator, we conclude that a nonFermi liquid develops as soon as the system is doped away from integer valence. The transformation is applied to a halffilled spin 3/2 Mott insulator as an example of the case of even valence and to the doped halffilled Hubbard model for the case of odd valence.
