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  • 1
    Electronic Resource
    Electronic Resource
    Polaron formation and hopping conductivity in the Holstein-Hubbard model (1994)
    Springer
    The European physical journal 94 (1994), S. 91-100 
    Details
    ISSN: 1434-6036
    Keywords: 63.20.Kr ; 71.38.+i ; 72.90.+y
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract On the basis of the Holstein-Hubbard model the formation of polarons at finite densities is investigated by means of a variational approach appropriate for describing squeezing and correlation effects. An effective Hubbard model for the polarons is derived, where the correlations are treated within the slave-boson saddlepoint approximation. For low enough phonon frequencies, with increasing coupling an abrupt self-trapping transition from light to heavy polarons is found. With increasing density the squeezing effect increases, and the transition is shifted to higher couplings. In the case of an effective Coulomb repulsion, the self-trapping transition is shifted to lower couplings with increasing Hubbard interaction, and the effective polaron mass below the transition is enhanced. In the heavy polaron regime, the frequency-dependent polaron hopping conductivity is calculated. There occur qualitative finite-density and correlation effects on the zero-temperature absorption spectrum which are discussed with respect to their possible relevance to the midinfrared absorption in high-T c superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307659
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Superconductivity mediated by the lattice fluctuations in the polaron system (1994)
    Springer
    The European physical journal 96 (1994), S. 149-158 
    Details
    ISSN: 1434-6036
    Keywords: 74.20.-z ; 71.38.+i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The coupling between the charge transfer and the lattice fluctuations is proposed as a possible mechanism of the superconductivity in the polaron system near the cross-over from the quasi-localized to the delocalized regime. The corresponding self-energy matrix is deduced using the Holstein Hamiltonian and the equations for the off-diagonal order are formulated. The lower bound on the superconducting critical temperature is estimated and the possible relevance of the proposed mechanism for the superconducting copper oxides is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313279
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Macromolecular cholesteric order observed by electron microscopy (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 439-445 
    Details
    ISSN: 0887-6266
    Keywords: cholesteric order ; electron microscopy ; periodical lamellar structure ; macromolecules ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The macromolecular cholesteric structure in the ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid [AA] cholesteric liquid crystalline solutions is studied by directly observing the morphology and structure of the ethyl-cyanoethyl cellulose [(E-CE)C]/polyacrylic acid [PAA] using electron microscopy. A periodical lamellar structure is observed in ultrathin slices of the composites with cholesteric order by both transmission electron microscopy (TEM) and low-voltage scanning electron microscopy (LVSEM). It is suggested that the periodical lamellar structure is induced by the twist of the molecular orientation in the cholesteric phase and reflects the structural features of the macromolecular cholesteric phase. The macromolecular cholesteric phase exhibits the twisted ring morphology in the initial stage of the formation of the liquid crystalline phase. The swelling of the ultrathin slices with cholesteric order in water is heterogeneous, which suggests the tight packing of the (E-CE)C chains in the direction of the helix axis in the macromolecular cholesteric phase. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 439-445, 1998
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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