91 research outputs found
Critical temperature for the two-dimensional attractive Hubbard Model
The critical temperature for the attractive Hubbard model on a square lattice
is determined from the analysis of two independent quantities, the helicity
modulus, , and the pairing correlation function, . These
quantities have been calculated through Quantum Monte Carlo simulations for
lattices up to , and for several densities, in the
intermediate-coupling regime. Imposing the universal-jump condition for an
accurately calculated , together with thorough finite-size scaling
analyses (in the spirit of the phenomenological renormalization group) of
, suggests that is considerably higher than hitherto assumed.Comment: 5 pages, 6 figures. Accepted for publication in Phys. Rev.
Signatures of Spin and Charge Energy Scales in the Local Moment and Specific Heat of the Two-Dimensional Hubbard Model
Local moment formation driven by the on--site repulsion is one of the
most fundamental features in the Hubbard model. At the simplest level, the
temperature dependence of the local moment is expected to have a single
structure at , reflecting the suppression of the double occupancy. In
this paper we show new low temperature Quantum Monte Carlo data which emphasize
that the local moment also has a signature at a lower energy scale which
previously had been thought to characterize only the temperatures below which
moments on {\it different} sites begin to correlate locally. We discuss
implications of these results for the structure of the specific heat, and
connections to quasiparticle resonance and pseudogap formation in the density
of states.Comment: 13 pages, 19 figure
Doping-dependent study of the periodic Anderson model in three dimensions
We study a simple model for -electron systems, the three-dimensional
periodic Anderson model, in which localized states hybridize with
neighboring states. The states have a strong on-site repulsion which
suppresses the double occupancy and can lead to the formation of a Mott-Hubbard
insulator. When the hybridization between the and states increases, the
effects of these strong electron correlations gradually diminish, giving rise
to interesting phenomena on the way. We use the exact quantum Monte-Carlo,
approximate diagrammatic fluctuation-exchange approximation, and mean-field
Hartree-Fock methods to calculate the local moment, entropy, antiferromagnetic
structure factor, singlet-correlator, and internal energy as a function of the
hybridization for various dopings. Finally, we discuss the relevance of
this work to the volume-collapse phenomenon experimentally observed in
f-electron systems.Comment: 12 pages, 8 figure
Caracterização da diversidade genĂ©tica de ovinos Santa InĂȘs em fazendas do Estado do PiauĂ
MODELING AND SIMULATION OF RELIEF INFLUENCE ON EUCALYPTUS FORESTS: INTERACTION BETWEEN SOLAR IRRADIANCE AND PRODUCTIVITY
History of registered Gyr breed in Brazilian Northeast: population structure and genetic improvement of growth traits
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