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  • 1
    Electronic Resource
    Electronic Resource
    Collective density fluctuations in heavy-fermion systems (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3673-3675 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Density fluctuations in heavy-fermion systems are discussed. Particular attention is paid to the hydrodynamic modes and it is pointed out how they differ from those of ordinary metals. A large Landau–Placzek ratio should help to make the quasiparticle diffusion mode observable. The role of the Coulomb interaction is discussed and it is shown that a low-lying optical plasmon should exist. The latter can be overdamped. It compliments the acoustic plasmon (or zero sound) mode into which the quasiparticle diffusion mode goes over for q values outside the hydrodynamic regime. In a recent experiment quasielastic light scattering due to density fluctuations has been observed in UPt3. Furthermore, it is shown that the attenuation mechanism of longitudinal ultrasound in heavy-fermion systems is very different from that of ordinary metals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340682
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  • 2
    Electronic Resource
    Electronic Resource
    Enhancement of Regeneration of the Saphenous Nerve after Treatment with Vitamins B1, B6, and B12 after Cold Lesion in the Rabbit (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 585 (1990), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1990.tb28080.x
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  • 3
    Electronic Resource
    Electronic Resource
    Density fluctuations in heavy fermion systems (1987)
    Springer
    The European physical journal 67 (1987), S. 35-41 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show explicitly that the hydrodynamic density modes of a heavy fermion system in the presence of long range Coulomb interactions can be reduced to those of an effective Hamiltonian used previously. Outside the hydrodynamic regime one finds acoustic plasmon (or zero sound) excitations as well as high energy plasmons. When the Fermi level intersects more than one heavy quasiparticle band, a situation which is expected to occur in most cases, then also a low-energy optical plasmon excitation should exist. The latter can be overdamped under special conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307305
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrodynamic fluctuations in heavy fermion systems (1987)
    Springer
    The European physical journal 65 (1987), S. 313-322 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A theory of hydrodynamic fluctuations in heavy fermion systems is presented. It is used to compute the attenuation and velocity of longitudinal ultrasound. The attenuation is dominated by the coupling of phonons to electronic density fluctuations. A discrepancy is resolved between theory and experiments on UPt3, which has been existing with respect to the absolute magnitude of the temperature dependent attenuation. The latter provides direct proof for a large Fermi liquid parameterF 0 s . The phonon Green's function is found to have a four-pole structure, resulting in two diffusive modes. One is the conventional one due to heat diffusion while the other is due to electron density diffusion and is a characteristic feature of heavy fermion systems. The two modes are coupled at finite temperatures. With the help of a model Hamiltonian (slave boson mean-field formulation of the Anderson lattice Hamiltonian) the ultrasound attenuation is calculated for low temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01303717
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  • 5
    Electronic Resource
    Electronic Resource
    Renormalization of the electron-phonon interaction: a reformulation of the BCS-gap equation (2003)
    Springer
    The European physical journal 33 (2003), S. 391-396 
    Details
    ISSN: 1434-6036
    Keywords: 71.10.Fd Lattice fermion models ; 74.20.Fg BCS theory and its development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A recently developed renormalization approach is used to study the electron-phonon coupling in many-electron systems. By starting from an Hamiltonian which includes a small gauge symmetry breaking field, we directly derive a BCS-like equation for the energy gap from the renormalization approach. The effective electron-electron interaction for Cooper pairs does not contain any singularities. Furthermore, it is found that phonon-induced particle-hole excitations only contribute to the attractive electron-electron interaction if their energy difference is smaller than the phonon energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2003-00180-9
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  • 6
    Electronic Resource
    Electronic Resource
    Beeinflussung der degenerativen und regenerativen Vorgänge an peripheren Nerven unter Behandlung mit B-Vitaminen (1990)
    Springer
    Journal of molecular medicine 68 (1990), S. 146-148 
    Details
    ISSN: 1432-1440
    Keywords: Peripheral nerve lesion by cold ; Vitamin B1, B6, B12-treatment ; Morphology ; Enhancement of nerve regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Degenerative and regenerative changes in the saphenous nerve of the rabbit following systemic treatment with either a combination of the vitamins B1, B6 und B12 or physiological saline solution were investigated. Cold lesion of the nerve (−196°C), which led to an optimal axonotmesis, was used to cause a secondary degeneration. The nerves were removed and investigated by light and electron microscopy after 4, 10 and 21 days. Morphological results show that the number of regenerating axons is higher and that of degenerating axons lower in the group treated with the given doses of vitamins than in the comparable control group. An explanation of the underlying metabolic processes is as yet not possible. Further investigations considering the contribution of the individual vitamins to the enhancement of degenerative and regenerative processes are necessary. Clinical indications of neurotoxicity due to the dose levels used here were not observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01646864
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  • 7
    Electronic Resource
    Electronic Resource
    Ground-state energy of strongly correlated electronic systems (1988)
    Springer
    The European physical journal 72 (1988), S. 423-427 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We calculate the ground-state energy of strongly correlated electrons by using a twodimensional (CuO2)N system as an example. It constitutes the most important structural element of the high-T c superconducting materials. The strong correlations are treated by projection technique. For that purpose a new form of the free energy is derived, which allows for applying that method. The ground-state energy for the half-filled band case is calculated by using a Padé approximation which agrees with series expansions up to order (t/(ε p −ε d ))6. Heret is thep-d hopping matrix element and ε p , ε d are the orbital energies of the O(2p x(y)) and $$Cu(3d_{x^2 - y^2 } )$$ electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01314521
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  • 8
    Electronic Resource
    Electronic Resource
    On the spectral function of a hole in a one-dimensional quantum antiferromagnet (1989)
    Springer
    The European physical journal 76 (1989), S. 473-482 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the spectral function of a single hole moving in a one-dimensional quantum antiferromagnet. The latter is described by an anisotropic version of thet-J model, wheret is the hopping matrix element. We introduce two independent coupling parametersJ ‖ andJ ⊥ for the Ising and the transverse part of the Heisenberg exchange. Strong electronic correlations which are incorporated in the model prevent the use of usual diagrammatic techniques for dynamic Green functions based on Wick's theorem. For that reason a new projection technique for general correlation functions in terms of cumulants is used. We consider the case of max . For the case of small transverse coupling relative to the Ising part, we give exact expressions for the one hole correlation function. In the limit of vanishing spin fluctuations our result reduces to earlier calculations of the motion of a hole in a one-dimensional Néel state. However, the inclusion of the spin fluctuations leads to drastic modifications of the spectral function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307897
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  • 9
    Electronic Resource
    Electronic Resource
    Coupling of electrons and phonons in a doped antiferromagnet (1992)
    Springer
    The European physical journal 89 (1992), S. 327-334 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is well-known that low-energy electronic excitations in high-T c superconductors have energies of the order of the exchange couplingJ, i.e. of the same order as the phonon energies. Therefore, low-energy electronic excitations and phonons should strongly influence each other. To investigate this problem we consider a coupled electron-phonon system. For the electronic degrees of freedom we start from the three band Hubbard or Emery model. In analogy to the transformation of the three band Hubbard model to thet−J model, studied by Zhang and Rice, we derive an effective electron-phonon interaction. Its electronic degrees of freedom are those of thet−J model which couple to the phonons of the original system. The coupling of electrons and phonons is discussed by means of the phonon Green function for a breathing-like mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01318164
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  • 10
    Electronic Resource
    Electronic Resource
    On the hole spectral function of the Emery model (1990)
    Springer
    The European physical journal 81 (1990), S. 165-173 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the spectral function of a single O hole generated in a two-dimensional CuO2-lattice at half-filling. The latter constitutes the most important structural element of high-T c superconducting materials. The system is described by the so-called extended Hubbard or Emery model. Strong electronic correlations which are incorporated in the model prevent the usual evaluation of Green functions based on Wick's theorem and using diagram techniques. For that reason we apply a new cumulant approach to dynamical correlation functions introduced recently. As a result we find that the local one-O hole excitation spectrum has two structured absorption regions around the bare O energyɛ p and aroundɛ p +Δ due to charge fluctuations of Cu holes. Here Δ is the bare charge transfer gap. The width of the absorption regime aroundɛ p is of the order of several timest pd 2 /Δ, wheret pd is the hopping integral between Cu and O holes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01309345
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