Romuald Lemanski

Stripe Phases in the Two-Dimensional Falicov-Kimball Model

The observation of charge stripe order in the doped nickelate and cuprate materials has motivated much theoretical effort to understand the underlying mechanism of the stripe phase. Numerical studies of the Hubbard model show two possibilities: (i) stripe order arises from a tendency toward phase separation and its competition with the long-range Coulomb interaction or (ii) stripe order inherently arises as a compromise between itinerancy and magnetic interactions. Here we determine the restricted phase diagram of the two-dimensional Falicov-Kimball model and see that it displays rich behavior illustrating both possibilities in different regions.

Model of charge and magnetic order formation in itinerant electron systems

We propose a simple model of charge and/or magnetic order formation in systems containing both localized and itinerant electrons coupled by the on-site, spin-dependent interaction that represents Coulomb repulsion and Hunds rule (a generalized Falicov-Kimball model). Ground state properties of the model are analyzed on the square lattice on a basis of the phase diagrams that have been constructed rigorously, but in a restricted configurational space. For intermediate values of the coupling constants there are considerable ranges of itinerant electron densities where phases with complex charge and magnetic structures of the localized electrons have lower energy than the simplest antiferro- and ferromagnetic ones. A strong tendency towards the antiferromagnetic coupling between spins of localized electrons has been observed close to half-filling for any density of localized electrons, including situations where the magnetic ions are diluted. For small band fillings the ferromagnetic coupling between localized spins is predominant.

Improving the efficiency of ultracold dipolar molecule formation by first loading onto an optical lattice

Ultracold ground-state dipolar

Ground states of the Falicov-Kimball model with correlated hopping

^{40}\mathrm{K}

Pattern formation in mixtures of ultracold atoms in optical lattices.

^{87}\mathrm{Rb}

Segregation and charge-density-wave order in the spinless Falicov-Kimball model

molecules recently have been produced in a loose harmonic trap by employing a magnetic field sweep across a Feshbach resonance followed by stimulated Raman adiabatic passage [K.-K. Ni et al., Science 322, 231 (2008)]. The overall experimental efficiency for molecule formation was around

Ground-state phase diagrams of the generalized Falicov-Kimball model with Hund coupling

20%

The asymmetric Hubbard model on a two-dimensional cluster

. We show that the efficiency can be increased to nearly

Momentum distribution and ordering in mixtures of ultracold light- and heavy-fermion atoms

100%