Roman Micnas

TL;DR: In this paper, the authors review the thermodynamic and electromagnetic properties of such systems in several limiting scenarios: (i) systems with on-site pairing which can be described by the extended negative-$U$ Hubbard model, at which it reduces to a system of tightly bound electron pairs (bipolarons) on a lattice, and the changeover from weak-attraction BCS-like superconductivity to the superfluidity of charged hard core bosons is examined.

TL;DR: A generalized periodic Anderson model with on-site hybridization between wide- and narrow-band electrons and strong and local coupling with the lattice deformation is studied and an effective Hamiltonian is obtained which describes a contact interaction between local pairs and wide- band electrons as well as the direct hopping of local Pair hopping and interparticle Coulomb interactions.

TL;DR: In this paper, the authors used a canonical transformation to derive an effective extended Hubbard Hamiltonian with intra-atomic repulsion and Ising-type interatomic exchange interaction in an effective external magnetic field from the extended Hubbard model with intra atomic attraction.

TL;DR: A simple model for superconductivity based on the extended Hubbard model with on-site repulsive and intersite attractive interaction for arbitrary electron density using the mean-field approach is studied.

TL;DR: It turns out that the two-band feature of the one-particle spectral function is reasonably well described by an ansatz for {ital A}(k,{omega}), which satisfies the first four frequency moments.