The Pseudoparticle Approach to Strongly Correlated Electron Systems
Résumé
The most prominent pseudoparticle representations and their applications to correlated spin and electronic models are reviewed, with approximate solution schemes ranging from saddle-point approximations with Gaussian fluctuations to conserving approximations and renormalization group (RG) techniques. Merits and shortcomings of these methods are described. In particular, the generic feature of radial slave boson fields to possess a finite expectation value is discussed, while pure fluctuation fields may best be treated by conserving approximations. We present applications to the magnetic phases of the Anderson lattice model and to the Hubbard model. The noncrossing approximation and the conserving T-matrix approximation are presented and discussed as the most important conserving approximations. Furthermore RG techniques for pseudoparticle representations, including “poor man’s scaling” and functional RG for the Kondo model in and out of equilibrium, a novel RG approach to the Kondo model for strong coupling, and the functional RG approach to frustrated Heisenberg models are discussed.