Superexchange in Dilute Magnetic Dielectrics: Application to (Ti,Co)O_2

We extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO_2 doped with transition metal impurities in cation sublattice. We suppose that ferromagnetic order arises due to superexchange between complexes [oxygen vacancies + magnetic impurities], which are stabilized by charge transfer from vacancies to impurities. The Hund rule controls the superexchange via empty vacancy related levels so that it becomes possible only for the parallel orientation of impurity magnetic moments. The percolation threshold for magnetic ordering is determined by the radius of vacancy levels, but the exchange mechanism does not require free carriers. The crucial role of the non-stoichiometry in formation of the ferromagnetism makes the Curie temperatures extremely sensitive to the methods of sample preparation.Comment: 18 pages, 2 figure

Electronic Structure Calculations of Magnetic Exchange Interactions in Europium Monochalcogenides

Using a combination of local spin density and Hubbard 1 approximations we study the mechansim of exchange interacion in EuX (X=O, S, Se and Te). We reproduce known experimental results about bulk modulus, critical pressure for structural phase transition, magnetic ordering temperature, spin--wave dispersions as well as momentum-- and tempearuture--dependent band shift. Our numerical results show pressure induced competition between the hybirization enhanced exchange interaction and Kondo--like coupling in EuO. Possible ways to enhance T_{c} are discussed

Slave boson theory of the extended Falicov-Kimball model

The extended Falicov-Kimball model, with both an on-site hybridization potential and dispersive narrow band, is examined within the saddle-point approximation to the Kotliar-Ruckenstein slave boson theory. We first set the hybridization potential to zero and find that the phase diagram depends strongly upon the orbital structure: for degenerate orbitals, a correlated-insulating state is found at sufficiently strong interaction strengths, whereas a finite orbital energy difference can lead to discontinuous valence transitions. The obtained phase diagram is very sensitive to the presence of a finite hybridization potential. As in Hartree-Fock theory, we find an enhancement of the hybridization by the inter-orbital Coulomb repulsion. The more precise treatment of correlation effects, however, leads to large deviations from the Hartree-Fock results. In the limit of vanishing hybridization an excitonic insulator state is only found when the orbitals are degenerate, which restricts this phase to a much smaller parameter space than in other available mean-field theories.Comment: 23 pages, 10 figure

Collective Excitations and Stability of the Excitonic Phase in the Extended Falicov--Kimball Model

We consider the excitonic insulator state (often associated with electronic ferroelectricity), which arises on the phase diagram of an extended spinless Falicov--Kimball model (FKM) at half-filling. Within the Hartree--Fock approach, we calculate the spectrum of low-energy collective excitations in this state up to second order in the narrow-band hopping and/or hybridisation. This allows to probe the mean-field stability of the excitonic insulator. The latter is found to be unstable when the case of the pure FKM (no hybridisation with a fully localised band) is approached. The instability is due to the presence of another, lower-lying ground state and not to the degeneracy of the excitonic phase in the pure FKM. The excitonic phase, however, may be stabilised further away from the pure FKM limit. In this case, the low-energy excitation spectrum contains new information about the properties of the excitonic condensate (including the strongly suppressed critical temperature).Comment: 8 pages, LaTeX-Revtex, 3 PostScript figures, minor corrections. Phys. Rev. B, in pres

Hanbury Brown and Twiss interferometry at a free-electron laser

We present measurements of second- and higher-order intensity correlation functions (so-called Hanbury Brown and Twiss experiment) performed at the free-electron laser (FEL) FLASH in the non-linear regime of its operation. We demonstrate the high transverse coherence properties of the FEL beam with a degree of transverse coherence of about 80% and degeneracy parameter of the order 10^9 that makes it similar to laser sources. Intensity correlation measurements in spatial and frequency domain gave an estimate of the FEL average pulse duration of 50 fs. Our measurements of the higher-order correlation functions indicate that FEL radiation obeys Gaussian statistics, which is characteristic to chaotic sources.Comment: 19 pages, 6 figures, 1 table, 40 reference

Сексуальность в структуре женской реализации

Стаття присвячена дослідженню особливостей жіночої сексуальної реалізації. Вивчення типології сексуальності та психосемантичного простору жінки дозволили визначити її генезис, структуру та механізми функціонування. В межах дослідження були виділені три жіночих типи сексуальності: маскулінний, залежний та істеричний.The article is devoted to research of features of female sexual realization. The study of sexuality typology and psychosemantic women’s space allowed to understand its genesis, structure and mechanisms of functioning. There were selected three female sexuality types: masculine, addictive and hysterical in research.Статья посвящена исследованию особенностей женской сексуальной реализации. Изучение типологии сексуальности и психосемантического пространства женщины позволили понять ее генезис, структуру и механизмы функционирования. В рамках исследования были выделены три женских типа сексуальности: маскулинный, зависимый и истеричный

Optical transition radiation in fused quartz under external acoustic field

In the present paper we have investigated the optical transition radiation in a plate excited by a longitudinal acoustic wave. The spectral-angular density of the radiated energy is calculated. The numerical examples are given for a plate of fused quartz. These results show that the acoustic waves allow to control the parameters of the radiation. In particular, new resonance peaks appear in the spectral distribution of the radiation intensity. The height of the peaks can be tuned by choosing the parameters of the acoustic wave

Kolmogorov analysis detecting radio and Fermi gamma-ray sources in cosmic microwave background maps

The Kolmogorov stochasticity parameter is shown to act as a tool to detect point sources in the cosmic microwave background (CMB) radiation temperature maps. Kolmogorov CMB map constructed for the WMAP's 7-year datasets reveals tiny structures which in part coincide with point radio and Fermi/LAT gamma-ray sources. In the first application of this method, we identified several sources not present in the then available 0FGL Fermi catalog. Subsequently they were confirmed in the more recent and more complete 1FGL catalog, thus strengthening the evidence for the power of this methodology.Comment: 4 pages, 3 figs, 1 Table; to match the published versio

LARGE-SCALE RESEARCH FACILITIES «MID-LATITUDE GEOPHYSICAL OBSERVATION COMPLEX «MIKHNEVO»

Presented here are the descriptions of the Large-Scale Research Facilities (LSRF) «Mid-latitude complex of geophysical observations "Mikhnevo"» at the Institute of Geospheres Dynamics of the Russian Academy of Sciences. The composition of the measuring complex, equipment and applied techniques are provided. The paper also presents some of the scientific results obtained at the LSRF «Mikhnevo» in recent years

УНИКАЛЬНАЯ НАУЧНАЯ УСТАНОВКА «СРЕДНЕШИРОТНЫЙ КОМПЛЕКС ГЕОФИЗИЧЕСКИХ НАБЛЮДЕНИЙ «МИХНЕВО»

Presented here are the descriptions of the Large-Scale Research Facilities (LSRF) «Mid-latitude complex of geophysical observations "Mikhnevo"» at the Institute of Geospheres Dynamics of the Russian Academy of Sciences. The composition of the measuring complex, equipment and applied techniques are provided. The paper also presents some of the scientific results obtained at the LSRF «Mikhnevo» in recent years.Представлено описание уникальной научной установки ИДГ РАН «Среднеширотный комплекс геофизических наблюдений "Михнево"». Описан состав измерительного комплекса, используемая аппаратура и применяемые методики. Кратко перечислены некоторые научные результаты, полученные на УНУ СКГН «Михнево» в последние годы