Now showing items 1-9 of 9

    • Approximate Treatment of a Two-Dimensional Anisotropic Peierls-Hubbard Model 

      Bernhard, Ben Hur; Iglesias, Jose Roberto (1993) [Journal article]
      A Green-function formalism is presented to study a Peierls-Hubbard Hamiltonian in two dimensions. The 1attice consists of parallel dimerized chains with alternating nearest-neighbor hoppings t and t 11 and another hopping ...
    • Eletronic and phonomic states of the Holstein-Hubbard dimer of variable length 

      Acquarone, C.; Iglesias, Jose Roberto; Gusmao, Miguel Angelo Cavalheiro; Noce, A.; Romano, Alfonso (1998) [Journal article]
      We consider a model Hamiltonian for a dimer of length a including all the electronic one- and two-body terms consistent with a single orbital per site, a free Einstein phonon term for a frequency V, and an electronphonon ...
    • From the atomic limit to a metal-insulator transition in the hubbard model 

      Craco, Luis; Gusmao, Miguel Angelo Cavalheiro (1995) [Journal article]
      Starting from the exact solution of the Hubbard model in the atomic limit, and treating the hopping term as a perturbation by means of a diagram technique, we discuss the electronic structure of the model in some simple ...
    • Green-Function Method for a Mixed-Valence Hamiltonian 

      Simoes, Acirete Souza da Rosa; Iglesias, Jose Roberto; Anda, Enrique V. (1984) [Journal article]
      A Green-function diagrammatic method is utilized to calculate the occupation number of a narrow (j) band in a mixed-valence system. The method is a generalization of the Hubbard-1 approximation for a two-band Hamiltonian. ...
    • Nature of insulating state in the three-band hubbard model : a tight-binding approach 

      Beatrici, Anderson; Gusmao, Miguel Angelo Cavalheiro (1995) [Journal article]
      We study the three-band Hubbard model, commonly used to describe the copper-oxygen planes of high-Tc superconductors, from the point of view of electronic properties. Utilizing perturbation theory around the atomic limit ...
    • Quantum critical behavior and thermodynamics of the repulsive one-dimensional Hubbard model in a magnetic field 

      Pâţu, Ovidiu I.; Klümper, Andreas; Foerster, Angela (2020) [Journal article]
      Even though the Hubbard model is one of the most fundamental models of highly correlated electrons, analytical and numerical data describing its thermodynamics at nonzero magnetization are relatively scarce. We present a ...
    • Solution of a two-leg spin ladder system 

      Links, Jon; Foerster, Angela (2000) [Journal article]
      A model for a spin-1/2 ladder system with two legs is introduced. It is demonstrated that this model is solvable via the Bethe ansatz method for arbitrary values of the rung coupling J. This is achieved by a suitable mapping ...
    • Tight-binding treatment of the Hubband model in infinite dimensions 

      Craco, Luis; Gusmao, Miguel Angelo Cavalheiro (1996) [Journal article]
      We discuss the infinite dimension limit of the Hubbard model by means of a perturbative expansion of the one-particle Green’s function around the atomic limit. The diagrammatic structure is simplified in this limit, allowing ...
    • Two-site Bose-Hubbard model with nonlinear tunneling : classical and quantum analysis 

      Lima, Diefferson Rubeni da Rosa de; Links, Jon; Isaac, Phillip S.; Foerster, Angela (2017) [Journal article]
      The extended Bose-Hubbard model for a double-well potential with atom-pair tunneling is studied. Starting with a classical analysis we determine the existence of three quantum phases: self-trapping, phase-locking, and ...