We apply the Coherent Potential Approximation (CPA) to an extended Hubbard model to describe disordered superconductors with d–wave pairing. We discuss the pair–breaking effect caused by non– magnetic disorder in presence of Van Hove singularity.

Using the self-consistent Born approximation, and the corresponding wave function of the magnetic polaron, we calculate the quasiparticle weight corresponding to destruction of a real electron (in contrast to creation of a spinless holon), as a funtion of wave vector for one hole in a generalized t − J model and the strong coupling limit of a generalized Hubbard model. The results are in excell...

We have studied finite-sized single band Hubbard chains with Fibonacci modulation for half filling within a mean field approximation. The ground state properties, together with the dc conductivity both at zero and non-zero temperatures, are calculated for such quasi-periodic Hubbard chains. While a reduction in the conductivity is found for strong electronic interaction or strong Fibonacci modu...

We derive the random-phase approximation for spin excitations in general multi-band Hubbard models, starting from a collinear ferromagnetic HartreeFock ground state. The results are compared with those of a recently introduced variational many-body approach to spin-waves in itinerant ferromagnets. As we exemplify for Hubbard models with one and two bands, the two approaches lead to qualitativel...

A slave-boson functional-integral method has been developed for the Hubbard model with arbitrary, orbital degeneracy D. Its saddle-point mean-field theory is equivalent to the Gutzwiller approximation, as in the case of single-band Hubbard model. Our theory is applied to the doubly degenerate (D = 2) model, whose paramagnetic state has been studied by numerical calculations. The effect of the e...

We investigate the dynamics of the one-dimensional strongly repulsive spin-1/2 Bose-Hubbard model for filling nu <or= 1. While at nu=1 the system is a Hubbard-Mott insulator exhibiting dynamical properties of the Heisenberg ferromagnet, at nu<1 it is a ferromagnetic liquid with complex spin dynamics. We find that close to the insulator-liquid transition the system admits for a complete separati...