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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3162-3167 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a microscopic derivation of the Fermi-liquid properties of the Anderson lattice. Our calculations suggest that the low-temperature state of the normal heavy Fermi liquid has a number of universal features, for which there is good experimental evidence. Using the Kondo-boson 1/N expansion, we find the Fermi liquid is characterized by the mean-field "bare'' particles (which are heavy) and their respective interactions. The latter are mediated by fluctuations in the f-level position and valence-conduction electron hybridization. Our calculations lead to the following experimental predictions: (i) the low-temperature specific heat behaves as C=γT∝T/TK with corrections ΔC=(T/TK)3 ln(T/TK), (ii) the zero-temperature spin susceptibility χ∝1/TK, and (iii) the resistivity ρ∝(T/TK)2. These results all contain a unique energy scale TK which is proportional to the inverse effective mass. Experimental support for these predictions is provided by evidence of systematic scaling of χ and ρ with γ throughout the entire class of heavy-fermion compounds. In addition we analyze recent pressure-dependent specific-heat measurements on UPt3 combined with χ and ρ data to confirm the scaling of these quantities with a single strongly pressure-dependent energy scale. This analysis provides evidence against current ferromagnetic spin-fluctuation theories.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2356-2361 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A theoretical analysis is provided of the anomalous isotope effects observed for the diffusion of hydrogen on the W(110) surface in the limit of zero coverage. Low temperature tunneling diffusion shows an isotope effect several orders of magnitude smaller than predicted by simple rigid lattice models, while the higher temperature activated diffusion displays an inverse isotope effect several orders of magnitude larger than the rigid lattice predictions. It is shown here that both effects can be explained consistently by a single model of hydrogen–tungsten interactions in which there is a large separation in time scales between the hydrogen and tungsten motions. Tunneling is described with a small polaron model. Large phonon overlap factors are found to diminish the role of the tunneling matrix element and thereby to decrease the isotope effect. Activated diffusion is described as a many-phonon process in which the vibron is thermally excited as a result of phonon–vibron coupling. The same coupling parameter explains both the tunneling and activated diffusion results. This coupling parameter is shown to be dependent on adsorbate mass.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5734-5739 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Schwinger boson representations allow us to study ferromagnetic and antiferromagnetic Heisenberg models in a rotationally invariant formulation. The large-N SU (N) Heisenberg models are approximated by the Schwinger boson mean-field theory (SBMFT). In most cases, even for N=2 (the physical model), the SBMFT is surprisingly successful: We review recent comparisons with numerical results, spin-wave theory, and renormalization group analysis of the nonlinear sigma model. The mean-field theory, like the nonlinear sigma model, does not include the effects of topological Berry phases, which can appear in the antiferromagnetic spin liquid phases.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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