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  • 1985-1989  (7)
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Material
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Year
  • 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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    Paper (German National Licenses)
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  • 2
    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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    Paper (German National Licenses)
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  • 3
    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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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Is there a molecular analogue of a Kondo singlet state? (1989)
    Springer
    The European physical journal 74 (1989), S. 277-278 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is suggested that molecules containing cerium ions with a formal valency +4 may form a ground state resembling a Kondo singlet. This is demonstrated explicitly by choosing cerocene as an example. Experimental consequences for these systems are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307872
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Electron correlations in hydrocarbon molecules (1985)
    Springer
    The European physical journal 60 (1985), S. 171-183 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An extensive investigation is made of electron correlations in the ground state of hydrocarbon molecules. This is done by starting from a semiempirical self-consistent field (SCF) calculation. The interatomic correlations are studied by means of a previously developed local approach to the correlation problem. It is demonstrated that the various contributions to the interatomic correlation energy can be described by simple analytical expressions which depend on the type of bond as well as on the bond lengths and angles. The results are easily understood in physical terms. The intraatomic correlations are obtained from an “atoms in molecules” type of approach as elaborated by Lievin et al. It makes use of a population analysis of the ground-state wave function as well as of calculations for the C and H atoms. We have then a very simple, and as it turns out rather accurate calculational scheme at hand. The computational times involved are of the same order as those for the fast SCF programs. As an application of the theory we have calculated the correlation energy difference between naphthalene and azulene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01304436
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    Paper (German National Licenses)
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  • 6
    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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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Strength of electron correlations in different types of chemical bonds (1987)
    Springer
    The European physical journal 66 (1987), S. 359-362 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A parameter is introduced which characterizes the strength of electron correlations in chemical bonds. It is calculated for a number of bonds. The results show that for a given type of bond (e.g. σ, isolated π, conjugated π, etc.) this parameter is almost independent of the types of atoms forming the bond. In contrast, the correlation energies are strongly dependent on the atoms forming the bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01305427
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    Paper (German National Licenses)
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