12 research outputs found
Non-Fermi liquid behavior in an extended Anderson model
An extended Anderson model, including screening channels (non-hybridizing,
but interacting with the local orbit), is studied within the Anderson-Yuval
approach, originally devised for the single-channel Kondo problem. By comparing
the perturbation expansions of this model and a generalized resonant level
model, the spin-spin correlation functions are calculated which show non-Fermi
liquid exponent depending on the strength of the scattering potential. The
relevance of this result to experiments in some heavy fermion systems is
briefly discussed.Comment: REVTEX, 17 pages, no figures, to be published in Phys. Rev.
A partition functional and thermodynamic properties of the infinite-dimensional Hubbard model
An approximate partition functional is derived for the infinite-dimensional
Hubbard model. This functional naturally includes the exact solution of the
Falicov-Kimball model as a special case, and is exact in the uncorrelated and
atomic limits. It explicitly keeps spin-symmetry. For the case of the
Lorentzian density of states, we find that the Luttinger theorem is satisfied
at zero temperature. The susceptibility crosses over smoothly from that
expected for an uncorrelated state with antiferromagnetic fluctuations at high
temperature to a correlated state at low temperature via a Kondo-type anomaly
at a characteristic temperature . We attribute this anomaly to the
appearance of the Hubbard pseudo-gap. The specific heat also shows a peak near
. The resistivity goes to zero at zero temperature, in contrast to
other approximations, rises sharply around and has a rough linear
temperature dependence above .Comment: 18 pages, 6 figures upon request, latex, (to appear in Phys. Rev. B
Thermal Properties of Carbon Nanotube–Copper Composites for Thermal Management Applications
Carbon nanotube–copper (CNT/Cu) composites have been successfully synthesized by means of a novel particles-compositing process followed by spark plasma sintering (SPS) technique. The thermal conductivity of the composites was measured by a laser flash technique and theoretical analyzed using an effective medium approach. The experimental results showed that the thermal conductivity unusually decreased after the incorporation of CNTs. Theoretical analyses revealed that the interfacial thermal resistance between the CNTs and the Cu matrix plays a crucial role in determining the thermal conductivity of bulk composites, and only small interfacial thermal resistance can induce a significant degradation in thermal conductivity for CNT/Cu composites. The influence of sintering condition on the thermal conductivity depended on the combined effects of multiple factors, i.e. porosity, CNTs distribution and CNT kinks or twists. The composites sintered at 600°C for 5 min under 50 MPa showed the maximum thermal conductivity. CNT/Cu composites are considered to be a promising material for thermal management applications