arXiv subjects

J. M. B. Lopes dos Santos

Publications and source records attributed to J. M. B. Lopes dos Santos.

43 records · Page 3Linked to original sources

arXiv2004

One-Electron Singular Branch Lines of the Hubbard Chain

The momentum and energy dependence of the weight distribution in the vicinity of the one-electron spectral-function singular branch lines of the 1D Hubbard model is studied for all values of the electronic density and on-site repulsion $U$. To achieve this goal we use the recently introduced pseudofermion dynamical theory. Our predictions agree quantitatively for the whole momentum and energy bandwidth with the peak dispersions observed by angle-resolved photoelectron spectroscopy in the quasi-1D organic conductor TTF-TCNQ.

cond-mat.str-el↗

arXiv2004

Double Exchange Model for Magnetic Hexaborides

A microscopic theory for rare-earth ferromagnetic hexaborides, such as Eu(1-x)Ca(x)B6, is proposed on the basis of the double-exchange Hamiltonian. In these systems, the reduced carrier concentrations place the Fermi level near the mobility edge, introduced in the spectral density by the disordered spin background. We show that the transport properties such as Hall effect, magnetoresitance, frequency dependent conductivity, and DC resistivity can be quantitatively described within the model. We also make specific predictions for the behavior of the Curie temperature, Tc, as a function of the plasma frequency, omega_p.

cond-mat.str-el↗

arXiv2004

Exact Solution of Ising Model on a Small-World Network

We present an exact solution of a one-dimensional Ising chain with both nearest neighbor and random long-range interactions. Not surprisingly, the solution confirms the mean field character of the transition. This solution also predicts the finite-size scaling that we observe in numerical simulations.

cond-mat.stat-mech↗

arXiv2002

Dipolar interactions and anisotropic magnetoresistance in metallic granular systems

We revisit the theory of magnetoresistance for a system of nanoscopic magnetic granules in metallic matrix. Using a simple model for the spin dependent perturbation potential of the granules, we solve Boltzmann equation for the spin dependent components of the non equilibrium electronic distribution function. For typical values of the geometric parameters in granular systems, we find a peculiar structure of the distribution function of conduction electrons, which is at variance with the two-current model of conduction in inhomogeneous systems. Our treatment explicitly includes the effects of dipolar correlations yielding a magnetoresistance ratio which contains, in addition to the term proportional to the square of uniform magnetization (< {\boldsymbol μ} >), a weak anisotropic contribution depending on the angle between electric and magnetic fields, and arising from the anisotropic character of dipolar interactions.

cond-mat.mtrl-sci↗

arXiv1999

One-Particle Spectral Properties of 1D Mott-Hubbard Insulators

We use an exact {\it holon} and {\it spinon} Landau-liquid functional which describes the holon - spinon interactions at all scattering orders, to study correlation functions of integrable multicomponent many-particle problems showing both linear and non-linear energy bands. Motivated by recent photoemission experiments, we consider specific cases when the dominant non-linear band terms are quadratic and apply our results to the evaluation of the half-filling 1D Hubbard model one-particle spectral functions beyond conformal-field theory.

cond-mat.str-el↗

arXiv1999

One-Particle Spectral Properties of Mott-Hubbard Insulators

We use an exact holon and spinon Landau-liquid functional which describes the holon - spinon interactions at all scattering orders, to study correlation functions of integrable multicomponent many-particle problems showing both linear and non-linear energy bands. We consider specific cases when the dominant non-linear band terms are quadratic and apply our results to the evaluation of the 1D Hubbard model correlation functions beyond conformal-field theory.

cond-mat.str-el↗

arXiv1998

Electronic spectrum and hopping conductivity in highly doped lattice systems

A model of strongly disordered lattice system with long-range Coulomb interactions between localized charge carriers has been considered. The total electronic energy is characterized by the presence of multiple metastable minima (including the true ground state), and different types of excitation spectra over these minima. A numeric procedure, accounting for all many-body correlations in finite size samples, confirms the existence of Coulomb gap in the single-particle spectrum and also provides corrections to the known mean-field theory results, as asymmetry of the gap at non-half-filling, vanishing density of low energy pair excitations, modified temperature exponent for hopping conductivity.

cond-mat.str-el↗