It is shown that at low densities, quantum dots with few electrons may be mapped onto effective charge-spin models for the low-energy eigenstates. This is justified by defining a lattice model based on a many-electron pocketstate basis in which electrons are localised near their classical ground-state positions. The equivalence to a single-band Hubbard model is then established leading to a cha...

The self-consistent theory of Singwi, Tosi, Land and Sjolander (STLS), which accounts for exchange and short-range correlation effects through an effective potential depending on the structure factor, is generalized to the Visscher and Falicov model of the layered electron gas. The complete numerical solution of the STLS self-consistent equations provides information about intraplane and inter...

Using the description in terms of the Hubbard operators hole and spin Green’s functions of the two-dimensional t-J model are calculated in an approximation which retains the rotation symmetry of the spin susceptibility in the paramagnetic state and has no predefined magnetic ordering. In this approximation, Green’s functions are represented by continued fractions which are interrupted with the ...

The electronic structure of NaxCoO2 revealed by recent photoemission experiments shows important deviations from band theory predictions. The six small Fermi surface pockets predicted by local-density approximation calculations have not been observed as the associated e'(g) band fails to cross the Fermi level for a wide range of sodium doping concentration x. In addition, significant bandwidth ...

We develop two methods to calculate the momentum distribution of the insulating Mott and charge-densitywave phases of the extended Bose-Hubbard model with on-site and nearest-neighbor boson-boson repulsions on d-dimensional hypercubic lattices. First, we construct the random-phase approximation result, which corresponds to the exact solution for the infinite-dimensional limit. Then, we perform ...

Phase diagrams of the two-dimensional one-band t-t8 Hubbard model are obtained within the two-patch and temperature-cutoff many-patch renormalization group approaches. At small t8 and at van Hove band fillings antiferromagnetism dominates, while with increasing t8 or changing filling antiferromagnetism is replaced by d-wave superconductivity. Near t85t/2 and close to van Hove band fillings the ...

The semiclassical and quantum dynamics of two ultrastrongly coupled nonlinear resonators cannot be explained using the discrete nonlinear Schrödinger equation or the Bose-Hubbard model, respectively. Instead, a model beyond the rotating wave approximation must be studied. In the semiclassical limit this model is not integrable and becomes chaotic for a finite window of parameters. For the quant...

I address here the question of the mutual interplay of strong correlations and disorder in the system. I consider random version of the Hubbard model. Diagonal randomness is introduced via random on-site energies and treated by the coherent potential approximation. Strong, short ranged, electron electron interactions are described by the slave boson technique and found to induce additional diso...

We consider the Hubbard model for electrons in a two-dimensional quasiperiodic tiling using the Hartree–Fock approximation. Numerical solutions are obtained for the first three square approximants of the perfect octagonal tiling. At half-filling, the magnetic state is antiferromagnetic. We calculate the distributions of local magnetizations and their dependence on the local environments as U is...

We investigate exciton-photon quantum phase transitions in a planar lattice of one-mode cavities containing one quantum dot. The quantum dot can be occupied by up to two excitons with opposite spin. We adopt the well-established mean-field approximation comprising an exciton order parameter and a photon coherence parameter. Calculating excitonand photon-phase diagrams it is demonstrated that by...