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Hubbard Hamiltonian (hubbard + hamiltonian)

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Physics and Astronomy100%

Selected Abstracts

The properties of the CDW phase in the weak coupling anharmonic Holstein,Hubbard model

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006
P. GrzybowskiArticle first published online: 2 JAN 200
Abstract The anharmonic Holstein,Hubbard Hamiltonian in the case of weak effective electron,electron attraction is studied. To deal with anharmonicity of phonons, variational canonical transformations are used to derive an effective electron Hamiltonian. The properties of the charge density wave (CDW) phase, for half-filling, are analyzed using this effective Hamiltonian. In particular, the critical temperatures, gap function, order parameter and gap ratio are calculated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic properties of bimetallic Co-Pd nanostructures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2005
Javier Guevara
Abstract We study the dependence of the magnetic properties of Co-Pd nanoclusters (Co cores coated by Pd atoms) on size and relative composition. We consider Co-Pd clusters having closed shell cubo-octahedral structure with an increasing Co core size. The electronic and magnetic properties are calculated with a parametrized Hubbard Hamiltonian within the unrestricted Hartree-Fock approximation. We show that, depending on the relative composition, the Pd coating can give rise to an enhancement of the average magnetic moment of the Co core. We compare with results from slabs by using an ab initio calculation method. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Speed of sound in an optical lattice

ANNALEN DER PHYSIK, Issue 10 2010
Z. Koinov
Abstract A system of equal mixture of 6Li atomic Fermi gas of two hyperfine states loaded into a cubic three-dimensional optical lattice is studied assuming a negative scattering length (BCS side of the Feshbach resonance). When the interaction is attractive, fermionic atoms can pair and form a superfluid. The dispersion of the phonon-like mode and the speed of sound in the long-wavelength limit are obtained by solving the Bethe-Salpeter equations for the collective modes of the attractive Hubbard Hamiltonian. [source]

Optically driven Mott-Hubbard systems out of thermodynamic equilibrium

ANNALEN DER PHYSIK, Issue 12 2009
A. Lubatsch
Abstract We consider the Hubbard model at half filling, driven by an external, stationary laser field. This stationary, but periodic in time, electromagnetic field couples to the charge current, i.e. it induces an extra contribution to the hopping amplitude in the Hubbard Hamiltonian (photo-induced hopping). We generalize the dynamical mean-field theory (DMFT) for nonequilibrium with periodic-in-time external fields, using a Floquet mode representation and the Keldysh formalism. We calculate the non-equilibrium electron distribution function, the density of states and the optical DC conductivity in the presence of the external laser field for laser frequencies above and below the Mott-Hubbard gap. The results demonstrate that the system exhibits an insulator-metal transition as the frequency of the external field is increased and exceeds the Mott-Hubbard gap. This corresponds to photo-induced excitations into the upper Hubbard band. [source]