Quantum phase transition in a two-dimensional system of dipoles

The ground-state phase diagram of a two-dimensional Bose system with dipole-dipole interactions is studied by means of quantum Monte Carlo technique. Our calculation predicts a quantum phase transition from gas to solid phase when the density increases. In the gas phase the condensate fraction is calculated as a function of the density. Using Feynman approximation, the collective excitation branch is studied and appearance of a roton minimum is observed. Results of the static structure factor at both sides of the gas-solid phase are also presented. The Lindeman ratio at the transition point comes to be $\gamma = 0.230(6)$. The condensate fraction in the gas phase is estimated as a function of the density.Comment: 4 figures v.3 One citation added, updated Fig.4. Minor changes following referee's and editor's comment

Crystal Structures and Magnetic Properties of the A2MnTeO6 FAMILY (A = Li, Ni, Ag, Tl)

Neutron diffraction studies of powder samples from the A2MnTeO6 (A= Li, Na, Ag, Tl) family of tellurates at room and low temperatures have been carried out. The features of the crystal structure were studied and the spin structure in the ordered state was determined for all compounds