T. K. Kopec

Quantum rotor description of the Mott-insulator transition in the Bose-Hubbard model

We present the novel approach to the Bose-Hubbard model using the

Néel order in the Hubbard model within a spin-charge rotating reference frame approach: Crossover from weak to strong coupling

\mathrm{U}(1)

Three-dimensional Josephson-junction arrays in the quantum regime

quantum rotor description. The effective action formalism allows us to formulate a problem in the phase only action and obtain an analytical formulas for the critical lines. We show that the nontrivial

Dependence of the superconducting critical temperature on the number of layers in a homologous series of high- T c cuprates

\mathrm{U}(1)

Superfluid-to-Mott transition in optical lattices with restricted geometry

phase field configurations have an impact on the phase diagrams. The topological character of the quantum field is governed by terms of the integer charges - winding numbers. The comparison presented results to recently obtained quantum Monte Carlo numerical calculations suggests that the competition between quantum effects in strongly interacting boson systems is correctly captured by our model.

Ground-state properties of charge and magnetically frustrated two-dimensional quantum Josephson junction arrays

The antiferromagnetic phase of two-dimensional (2D) and three-dimensional (3D) Hubbard model with nearest neighbor hopping is studied on a bipartite cubic lattice by means of the quantum

Temperature-dependent excitation spectra of ultra-cold bosons in optical lattices

\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)

Local dissipation effects in two-dimensional quantum Josephson junction arrays with a magnetic field

rotor approach that yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties of the model and satisfy the Mermin-Wagner theorem. The collective variables for charge and spin are isolated in the form of the space-time fluctuating U(1) phase field and rotating spin-quantization axis governed by the SU(2) symmetry, respectively. As a result interacting electrons appear as composite objects consisting of bare fermions with attached U(1) and SU(2) gauge fields. An effective action consisting of a spin-charge rotor and a fermionic field is derived as a function of the Coulomb repulsion

Competition between charge ordering and superconductivity in La2−xMxCuO4

U

Density of states and excitonic condensation in the double layer correlated systems

and hopping parameter