Magnetic ordering of itinerant systems in modified mean field theory: antiferromagnetism

We analyze the itinerant model for antiferromagnetism, which was developed previously by Plischke, Mattis, Brouers and Mizia. In this model we include both; single-site and two-site electron correlations. Including additionally band degeneration into the model allows for considering intra-atomic exchange interactions in the Hamiltonian. The modified Hartree-Fock approximation for the two-site interactions is used. This approximation gives the spin band narrowing, which is the same for both spin directions and affects possibility of antiferromagnetic ordering. We use the Green function technique and CPA decoupling. This allows for the change in shape of the spin bands, described by the correlation factors, which decreases kinetic energy of the system. The effective Hartree field and the gain in kinetic energy due to the on-site and inter-site correlation factors drive the antiferromagnetism.Comment: 8 pages, 1 figur

Muonic-atom scattering from hydrogenic liquids in an incoherent approach

The differential cross sections for low-energy muonic hydrogen atom scattering in liquid hydrogenic targets have been calculated in the incoherent approximation using the Van Hove response function. A simple model of liquids and the available experimental parameters have been employed for a description of the diffusive and vibrational modes in these targets. At collision energies below about 10 meV, the obtained cross sections are very different from the analogous cross sections for scattering in hydrogenic gases.Comment: 15 pages, 17 figure

Phase separation near half-filling point in superconducting compounds

We present the model of superconducting ceramics using the single band extended Hubbard Hamiltonian. We investigate the simultaneous presence of antiferromagnetism (AF) and d-wave superconductivity (SC) in the coherent potential (CP) approximation applied to the on-site Coulomb repulsion $U$. We consider the hopping interaction, $\Delta t$, the inter-site charge-charge interaction, $V$, (creating SC), and the single site Hund's type exchange interaction, $F_{in}$, (creating AF). The influence of these interactions on the separation of superconducting and antiferromagnetic phases near the half-filling point is investigated. Results are compared with the experimental data for YBaCuO and NdCeCuO compounds.Comment: 4 pages, 4 figure

Alternative equation of motion approach to the single-impurity Anderson model

Solving the single-impurity Anderson model (SIAM) is a basic problem of solid state physics. The SIAM model is very important, at present it is also used for systems with quantum impurities, e.g. semiconductor quantum dots and molecular transistors. Its main application is in the scheme of dynamical mean field theory (DMFT) describing strong correlation electron systems. To solve the SIAM problem we use the equation of motion (EOM) Green function approach. In this report we present the novel EOM approximation in which we differentiate the Green function over both time variables. This differs from the commonly used EOM solution by Appelbaum, Penn and Lacroix where the authors take time derivative only over primary time variable. After extending calculations to higher order Green functions we find the new approximate dynamical solution of SIAM. The results are compared with the solutions to the SIAM problem at intermediate Coulomb repulsion U such as the Modified Iterative Perturbation Theory. Our approach is suitable for describing quantum dots.Comment: 6 pages, 3 figure

Circular scans for CMB anisotropy observation and analysis

A number of experiments for measuring anisotropies of the Cosmic Microwave Background use scanning strategies in which temperature fluctuations are measured along circular scans on the sky. It is possible, from a large number of such intersecting circular scans, to build two-dimensional sky maps for subsequent analysis. However, since instrumental effects --- especially the excess low-frequency 1/f noise --- project onto such two-dimensional maps in a non-trivial way, we discuss the analysis approach which focuses on information contained in the individual circular scans. This natural way of looking at CMB data from experiments scanning on the circles combines the advantages of elegant simplicity of Fourier series for the computation of statistics useful for constraining cosmological scenarios,and superior efficiency in analysing and quantifying most of the crucial instrumental effects.Comment: 10 pages, 5 figures (.ps), submitted to MNRA