Navegação Produção Científica por Autor "Gusmao, Miguel Angelo Cavalheiro"
Resultados 1-20 de 35
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Band-filling and disorder effects in the ordered phase of the Falicov-Kimball model
(2014) [Artigo de periódico]We investigate the stability of “magnetic” ordering against band-filling changes and Anderson-like disorder in the Falicov-Kimball model, within dynamical mean-field theory (DMFT). The one-particle density of states is ... -
Band-filling effects on Kondo-lattice properties
(2003) [Artigo de periódico]We present theoretical results for a Kondo-lattice model with spin-1/2 localized moments, including both the intrasite Kondo coupling and an intersite antiferromagnetic exchange interaction, treated within an extended ... -
Bias dependence of magnetoresistance in Fe-Al/sub 2/O/sub 3/ granular thin films
(2002) [Artigo de periódico]This paper reports on the magnetotransport behavior of Fe–Al2O3 granular thin films when the injected dc current is varied. The electric resistance as a function of temperature, magnetoresistance, and the current vs applied ... -
Bicriticality in Fe/sub x/Co/sub 1-x/Ta/sub 2/O/sub 6/
(2003) [Artigo de periódico]X-ray and neutron-diffraction, dc magnetic susceptibility, magnetization, and specific-heat measurements are reported for FexCo1 xTa2O6 mixed oxides. X-ray refinement indicates homogeneous samples for all the reported ... -
Coupled dynamics of interacting spin-1 bosons in a double-well potential
(2018) [Artigo de periódico]We present a detailed analysis of dynamical processes involving two or three particles in a double-well potential. Motivated by experimental realizations of such a system with optically trapped cold atoms, we focus on ... -
Critical exponents of the disorder-driven superfluid-insulator transition in one-dimensional Bose-Einstein condensates
(2011) [Artigo de periódico]We investigate the nature of the superfluid-insulator quantum phase transition driven by disorder for noninteracting ultracold atoms on one-dimensional lattices. We consider two different cases: Anderson-type disorder, ... -
Crossover exponents for the potts model with quadratic symmetry breaking
(1984) [Artigo de periódico]The effect of quadratic symmetry breaking (QSB) on two representations for the Potts vectors in a continuum-field model are studied to two-loop order in renormalized perturbation theory in d=6-E dimensions, in extension ... -
De Haas-van Alphen oscillations and magnetic breakdown : semiclassical calculation of multiband orbits
(1998) [Artigo de periódico]We use an algebraic method to compute de Haas–van Alphen oscillations in two-dimensional systems in the semiclassical approximation for cases where the Fermi surface lies on more than one sheet of the energy surface. We ... -
Effect of band filling in the Kondo lattice : a mean-field approach
(1999) [Artigo de periódico]The usual Kondo lattice, including an antiferromagnetic exchange interaction between nearest-neighboring localized spins, is treated here in a mean-field scheme that introduces two mean-field parameters: one associated ... -
Effects of band filling in the Anderson-Falicov-Kimball model
(2013) [Artigo de periódico]In this work, we study the Anderson-Falicov-Kimball model within the dynamical mean field theory for the Bethe lattice, restricting our analysis to the nonmagnetic case. The one-particle density of states is obtained by ... -
Eletronic and phonomic states of the Holstein-Hubbard dimer of variable length
(1998) [Artigo de periódico]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 ... -
Fate of topological states in incommensurate generalized Aubry-André models
(2016) [Artigo de periódico]We study one-dimensional optical lattices described by generalized Aubry-André models that include both commensurate and incommensurate modulations of the hopping amplitude. This brings together two interesting features ... -
Finite-size effects in Anderson localization of one-dimensional Bose-Einstein condensates
(2010) [Artigo de periódico]We investigate the disorder-induced localization transition in Bose-Einstein condensates for the Anderson and Aubry-Andr´e models in the noninteracting limit using exact diagonalization. We show that, in addition to the ... -
Fluctuation conductivity of inhomogeneous superconductors : a fractal aggregation model
(1990) [Artigo de periódico]Numerical simulations of diffusion processes are performed on fractal aggregates designed to mimic the structure of inhomogeneous granular superconductors. The spectral dimensions obtained yield ftuctuation-conductivity ... -
Fluctuation magnetoconductivity in YBa/sub 2/Cu/sub 3/O/sub 7/ : Gaussian, three-dimensional XY, beyond three-dimensional XY, and lowest-Landau-level scaling
(2001) [Artigo de periódico]Systematic measurements of the in-plane fluctuation magnetoconductivity in a YBa₂Cu₃O₇ single crystal are presented. Fields between 0 and 14 T were applied either parallel or perpendicular to the Cu-O atomic planes. The ... -
From the atomic limit to a metal-insulator transition in the hubbard model
(1995) [Artigo de periódico]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 ... -
Generic model of the colossal magnetoresistance pyrochlore Tl/sub 2/Mn/sub 2/O/sub 7/
(2002) [Artigo de periódico]The colossal magnetoresistance (CMR) exhibited by the pyrochlore compound Tl₂Mn₂O₇ was discovered in 1996. Important differences with CMR Mn-perovskite compounds regarding crystal structure and electronic properties were ... -
Ground states of spin-1 bosons in asymmetric double wells
(2015) [Artigo de periódico]In this work we investigate the different states of a system of spin-1 bosons in two potential wells connected by tunneling, with spin-dependent interaction. The model utilizes the well-known Bose-Hubbard Hamiltonian, ... -
Low-dimensional magnetic properties of orthorhombic MnV2O6 : a nonstandard structure stabilized at high pressure
(2017) [Artigo de periódico] -
Magnetic and orbital ordering of RuO/sub 2/ planes in RuSr/sub 2/ (Eu,Gd) Cu/sub 2/O/sub 8/
(2004) [Artigo de periódico]We start from an effective Hamiltonian for Ru ions in a square lattice, which includes the on-site interactions between t2g orbitals derived from Coulomb repulsion, and a tetragonal crystal-field splitting. Using perturbation ...
