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    Wyświetlanie 1-8 z 8
    Tytuł:
    The Fock Term in the Charge Ordered Phase of the t-W Model
    Autorzy:
    Bak, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1427073.pdf
    Data publikacji:
    2012-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.45.Lr
    71.10.Fd
    71.27.+a
    71.30.+h
    Opis:
    The paper shows the importance of retaining Hartree and Fock terms, appearing after mean-field decoupling, in the treatment of charge ordered phase of the t-W model, with implications to extended Hubbard model.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 5-6; 1085-1088
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Charge Orderings and Phase Separations in Itinerant Fermion Systems at Half Filling
    Autorzy:
    Czart, W.
    Grzybowski, P.
    Nogala, M.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1426750.pdf
    Data publikacji:
    2012-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.30.+h
    71.45.Lr
    64.75.Gh
    Opis:
    We analyse the ground state phase diagrams of the charge orderings in narrow band materials using two effective models: (1) the spinless fermion model (t - W) with repulsive intersite interaction ($W_{ij}$ > 0) and (2) the molecular crystal model with the coupling of electrons to intramolecular (crystal field) vibrations. We present results for the case of half filled bands for d = 2 square lattice. The calculations are performed within the (broken symmetry) Hartree-Fock approximation. The study takes into consideration the effects of frustrating next-nearest-neighbour hopping $(t_2)$ on the charge ordered states in these systems. We focus on the two cases: (i) homogeneous phases and phase separations involving checkerboard charge ordering with the nesting vector Q= (π,π) only and (ii) homogeneous phases and phase separations involving two types of charge ordering: (a) checkerboard charge ordering with the nesting vector Q = (π,π), and (b) collinear (CL) charge ordering with Q = (0,π) or Q = (π,0).
    Źródło:
    Acta Physica Polonica A; 2012, 121, 5-6; 1042-1044
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effects of Frustrating Hopping on Charge Ordered States in Itinerant Fermion Systems for Arbitrary Concentration in 2D Lattice
    Autorzy:
    Czart, W.
    Grzybowski, P.
    Nogala, M.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1431325.pdf
    Data publikacji:
    2012-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.30.+h
    71.45.Lr
    64.75.Gh
    Opis:
    There is ongoing, intense, research in the field of electron charge orderings (CO) and charge density waves phenomena, due to experimental discovery of such phases in numerous important compounds. The aim of this work is to extend recent advances in the field by studying two simple effective paradigmatic models used to describe CO in narrow band materials i.e. (i) a model of correlated electrons: the so-called t-W model of spinless fermions with repulsive interaction W and (ii) the molecular crystal model with the coupling of electrons to intramolecular (crystal field) vibrations in the static limit. The finite temperature phase diagrams are evaluated at arbitrary carriers concentration for several representative cases. Our calculations are performed within the (broken symmetry) HFA for d=2 square lattice and arbitrary carriers concentration. In this contribution we focus on the effects of next-nearest-neighbor hopping on the CO states in these systems and the problem of phase separations involving checkerboard CO with the nesting vector Q=(π,π). The results we show here are an extension of our previous work on the subject.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 4; 828-831
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Interplay between Correlated Electrons and Quantum Phonons in Charge-Ordered and Mott-Insulating Organic Compounds
    Autorzy:
    Yonemitsu, K.
    Maeshima, N.
    Tanaka, Y.
    Powiązania:
    https://bibliotekanauki.pl/articles/1490009.pdf
    Data publikacji:
    2012-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.20.Bh
    71.30.+h
    71.45.Lr
    71.10.Fd
    Opis:
    At an early stage of the photoinduced transition from an insulator to a metal in quasi-two-dimensional organic conductors, a coherent motion of electrons is observed in a charge-ordered insulator, but not so far in a Mott insulator. The mechanisms of these different photoinduced charge dynamics are theoretically studied by numerical solutions to the time-dependent Schrödinger equation for exact many-electron-phonon wave functions on small clusters of model systems. We use two-dimensional three-quarter-filled extended Holstein-Hubbard models on anisotropic triangular lattices. For a charge-ordered insulator on a lattice simplified from the structure of $α-\text{(BEDT-TTF)}_2I_3$, we indeed find a low-energy collective electronic motion coupled with quantum phonons even if the energy of photoexcitation is away from this energy. For a Mott insulator on a lattice simplified from the structure of $κ-\text{(BEDT-TTF)}_2X$, however, such a collective motion does not appear, and quantum phonons are hardly excited.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 2; 372-374
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Charge Ordering and Phase Separations in the Spinless Fermion Model with Repulsive Intersite Interaction
    Autorzy:
    Czart, W.
    Robaszkiewicz, S.
    Tobijaszewska, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812286.pdf
    Data publikacji:
    2008-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.30.+h
    71.45.Lr
    64.75.Gh
    Opis:
    We study a simple effective model for description of charge orderings in narrow band materials, i.e. the spinless fermion model with repulsive intersite interaction W. The analysis is concentrated on the problem of phase separations and the effects of next-nearest neighbor hopping $t_2$ on the charge ordered states in this system. The cases of d-dimensional (d≥2) hypercubic lattices are considered for arbitrary particle concentration (0 < n < 1). Within the broken symmetry Hartree-Fock approximation the phase diagrams as a function of W and n are evaluated for representative cases. The results for $t_2$ ≠ 0 are compared with those found for the case with nearest neighbor hopping only.
    Źródło:
    Acta Physica Polonica A; 2008, 114, 1; 129-134
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Charge Ordering and Phase Separations in the Molecular Crystal Model
    Autorzy:
    Czart, W.
    Grzybowski, P.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1537090.pdf
    Data publikacji:
    2010-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.30.+h
    71.45.Lr
    64.75.Gh
    Opis:
    We analyse the ground state phase diagrams and thermodynamic properties of charge orderings in narrow band materials using the molecular crystal model in the static limit. We present results for the hypercubic lattices in dimensions d = 2 and d = ∞. We focus our study on the problem of phase separations involving charge orderings and the effects of next-nearest-neighbor hopping $(t_2)$ on the charge ordered states in these systems. The ground state phase diagrams are evaluated for a few representative cases. Results for the molecular crystal model are compared with those obtained previously for the spinless fermion model with repulsive intersite interaction W.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 2; 369-372
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Search for the Photo-Induced Hidden Phase in Inorganic and Organic Systems
    Autorzy:
    Koshihara, S.
    Onda, K.
    Okimoto, Y.
    Ishikawa, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/1489970.pdf
    Data publikacji:
    2012-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.47.J-
    63.20.kd
    71.30.+h
    71.45.Lr
    Opis:
    We review the dynamical behavior of strongly electron-lattice (orbital) coupled system induced by photo-excitation of fs laser pulse. By virtue of the femtosecond (fs) spectroscopy and picosecond (ps) time-resolved X-ray diffraction measurements, we demonstrate that the photo-irradiation creates new ordered state so called as "hidden phase" which can never be realized under thermo-equilibrium condition. This exotic phase commonly plays the key role for realizing the gigantic photo-induced changes in optical properties of inorganic and organic electron-lattice strongly coupled systems.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 2; 328-331
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Peierls Instability and Charge-Density-Wave Transport in Fluoranthene and Perylene Radical Cation Salts
    Autorzy:
    Brütting, W.
    Riess, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933357.pdf
    Data publikacji:
    1995-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.45.Lr
    71.30.+h
    72.10.Bg
    72.80.Le
    Opis:
    Fluoranthene and perylene radical cation salts are quasi-one-dimensional conductors, which show a Peierls transition to a charge-density-wave ground state. Radical cation salts with different stoichiometries composed of the aromatic donor molecules fluoranthene (Fa = C$\text{}_{16}$H$\text{}_{10}$) or perylene (Per = C$\text{}_{20}$H$\text{}_{12}$) and the counterion X¯ = PF¯$\text{}_{6}$ were investigated. We find that the temperature dependence of the electrical conductivity and the properties in the charge-density-wave ground state strongly depend on the composition of the crystals. When fluoranthene is replaced by perylene, the Peierls transition is shifted from 180 K to 120 K and the ground state energy gap decreases from values of 120-180 meV to 60-80 meV. In the charge-density-wave ground state the threshold field for nonlinear conductivity varies between 0.1 and 1 V/cm for different systems. Our results indicate that disorder, three-dimensional coupling and commensurability effects play an important role for the transport properties of these systems.
    Źródło:
    Acta Physica Polonica A; 1995, 87, 4-5; 785-790
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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