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We consider a classical, two-dimensional system of identical particles which interact via a finite-ranged, repulsive pair potential. We assume that the system is in a crystalline phase. We calculate the normal vibrational modes of a two-dimensional square Bravais lattice, first analytically within the nearest-neighbour approximation, and then numerically, relaxing the preceding hypothesis. We show that, in the harmonic approximation, the excitation of a transverse vibrational mode leads to the breakdown of the square lattice. We next study the case of the hexagonal Bravais lattice and we show that it can be stable with respect to lattice vibrations. We give a criterion determining whether or not it is stable in the nearest-neighbour approximation. Finally, we apply our results to a two-dimensional system of composite bosons and infer that the crystalline phase of such a system, if it exists, corresponds to a hexagonal lattice.
The ground-state phase properties of a two-dimensional Bose system with dipole-dipole interactions is studied by means of quantum Monte Carlo techniques. Limitations of mean-field theory in a two-dimensional geometry are discussed. A quantum phase tr
We investigate the physics of dipolar bosons in a two dimensional optical lattice. It is known that due to the long-range character of dipole-dipole interaction, the ground state phase diagram of a gas of dipolar bosons in an optical lattice presents
The competition between tunneling and interactions in bosonic lattice models generates a whole variety of different quantum phases. While, in the presence of a single species interacting via on-site interaction, the phase diagram presents only superf
We discuss the continuum limit of discrete Dirac operators on the square lattice in $mathbb R^2$ as the mesh size tends to zero. To this end, we propose a natural and simple embedding of $ell^2(mathbb Z_h^d)$ into $L^2(mathbb R^d)$ that enables us to
In this paper, we study the long time behavior of the solution of nonlinear Schrodinger equation with a singular potential. We prove scattering below the ground state for the radial NLS with inverse-square potential in dimension two $$iu_t+Delta u-