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  • 1990-1994  (6)
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  • 1
    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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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Simple approximation scheme for the Anderson impurity Hamiltonian (1991)
    Springer
    The European physical journal 83 (1991), S. 153-153 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01314410
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Simple approximation scheme for the Anderson impurity Hamiltonian (1990)
    Springer
    The European physical journal 79 (1990), S. 365-375 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A simple approximation scheme is presented for solving the Anderson impurity model within the Noncrossing Approximation (NCA). It is shown that with it the computations reduce to an extent that the scheme can be readily applied to interpret different experiments. The theory is applied to calculate the temperature dependence of the quadrupole moment and of the static and dynamic magnetic susceptibility. The effects of the crystalline electric field (CEF) are thereby incorporated. A comparison of the static susceptibility with exact Bethe ansatz results is given, when the effect of the CEF is neglected. Comparisons with the numerically exact solutions of the NCA are made where they are available. The application of the present theory to YbCu2Si2 is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437646
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Model for heavy-fermion behavior of Nd1.8Ce0.2CuO4 (1993)
    Springer
    The European physical journal 92 (1993), S. 133-135 
    Details
    ISSN: 1434-6036
    Keywords: 71.27.+a ; 71.28.+d ; 74.72.+h
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A model is proposed for the observed heavy-fermion like behavior of electron doped Nd2CuO4. It differs from the traditional description of heavy fermions because of the strong correlations between the conduction electrons. The effects of these correlations are simulated by breaking the spin symmetry. It is shown that the model can qualitatively account for the observed effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312167
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    On the ground state of the half-filled Hubbard model (1994)
    Springer
    The European physical journal 94 (1994), S. 335-339 
    Details
    ISSN: 1434-6036
    Keywords: 74.20.-Z ; 75.10.Jm ; 75.50.Ee
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We calculate the ground state of the half-filled Hubbard model and its energy by starting from a spindensity wave approximation and improving it by incorporating transverse spin fluctuations. The calculations are done by employing a projection method. The quality of the proposed approximation is particularly high for intermediate and large Coulomb repulsionU, where it exceeds considerably e.g. that of the Gutzwiller projected spin-density wave state. To ordert 2/U (wheret is the hopping matrix element), our approximation is shown to be equivalent to a recent Coupled Cluster calculation for the Heisenberg antiferromagnet. Finally we show how to ordert 2/U the linear spin-wave approximation for the Heisenberg antiferromagnet may be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320687
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Effective mass decrease due to electron-phonon interaction in heavy fermion systems (1993)
    Springer
    The European physical journal 90 (1993), S. 125-126 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is argued that in heavy fermion systems the electron-phonon interaction results in a decrease of the quasiparticle mass. This is in contrast to ordinary metals where this interaction is known to increase the effective mass. A simple expression is derived which relates the effective mass change to the electronic Grüneisen parameter, the Kondo temperature and the bulk modulus. For CeRu2Si2 the effective-mass decrease is estimated to be 25%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01321043
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    Paper (German National Licenses)
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