Experimental Raman and IR spectra of multiferroic [(CH3)2NH2][Ni(HCOO)3] were recorded at room temperature. The three-parameter hybrid B3LYP density functional method has been used with the 6-31G(d, p) basis set to derive the equilibrium geometry, atomic spin densities, vibrational wavenumbers, infrared intensities and Raman scattering activities. Based on these calculations, the assignment of ...

2014 X-ray diffuse scattering studies of one dimensional conductors (TMTSF)2ReO4 and (TMTSF)2NO3 reveal the formation of low temperature superstructures which might involve an ordering of the counter ions ReO-4 and NO-3. The superstructure reflections are characterized by wave vectors q = (1/2, 1/2, 1/2) for the perrhenate and q = (1/2, 0, 0) for the nitrate, which double the unit cell volume i...

Dynamical mean-field theory and its cluster extensions provide a very useful approach for examining phase transitions in model Hamiltonians and, in combination with electronic structure theory, constitute powerful methods to treat strongly correlated materials. The key advantage to the technique is that, unlike competing real-space methods, the sign problem is well controlled in the Hirsch-Fye ...

A novel order parameter Φ for spin glasses is defined based on topological criteria and with a clear physical interpretation. Φ is first investigated for well known magnetic systems and then applied to the Edwards-Anderson ±J model on a square lattice, comparing its properties with the usual q order parameter. Finite size scaling procedures are performed. Results and analyses based on Φ confirm...

The structure of single crystals of the organic metals aand /?-(BEDT-TTF)2I3* was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis. In the a-phase no unusual change of the room temperature unit cell but a slight variation in the triiodide network and especially a more pronounced dimerization i...

The phase diagram of the classical anisotropic (XXZ) Heisenberg model on the 2-dimensional triangular lattice is investigated using Monte Carlo methods. In the easy-axis limit, two finite temperature vortex unbinding transitions have been observed. In the easy-plane limit, there also appear to be two distinct finite temperature phase transitions which are very close in temperature. The upper tr...

Temperature dependent x-ray absorption spectra investigation were measured for Ba(1-x)K(x)BiO3 (Bi L3-edge) with x =0.0, 0.25, 0.4, 0.5 and for BaPbO3 (Pb L3-edge). It was found that at low temperatures the Debye-Waller factor of the square diagonal Bi-Bi bond has the maximum value near the insulator-metal phase transition for the compound with x = 0.25 and x = 0.4. Temperature dependence of th...

We solve a two-dimensional model for polymer chain folding in the presence of mechanical pulling force (f) exactly using equilibrium statistical mechanics. Using analytically derived expression for the partition function we determine the phase diagram for the model in the f-temperature (T) plane. A square root singularity in the susceptibility indicates a second order phase transition from a fo...

A class of binary mixtures of Janus fluids formed by colloidal spheres with the hydrophobic hemispheres constrained to point either up or down are studied by means of Gibbs ensemble Monte Carlo simulations and simple analytical approximations. These fluids can be experimentally realized by the application of an external static electrical field. The gas-liquid and demixing phase transitions in f...

In 1976 the North Pacific climate shifted, resulting in an average increase of the water temperature. In the Gulf of Alaska the climate shift was followed (i.e. early 1980s) by a gradual but dramatic increase in the abundance of groundfish species that typically prey on pre-recruitment stages of walleye pollock. In the present study we used a previously parameterized model to investigate the ef...