arXiv subjects
Publications and source records attributed to A. A. Gomes.
The magnetic properties of pure transition-like metals are discussed within the single site approximation, to take into account the electron correlation. The metal is described by two hybridized bands one of which includes the Coulomb correlation. Our results indicate that ferromagnetism follows from adequate values of the correlation and hybridization.
The Fermi surface (FS) of an extended $d-p$ Hubbard model is investigated by a two-pole approximation in both situations with hole and electron doping. Using the factorization procedure proposed by Beenen and Edwards, superconductivity with singlet $d_{x^2-y^2}$-wave pairing is considered. The effects of the $d-p$ hybridization on the FS are the main focus in the present work. Nevertheless, the asymmetries between the hole- and electron-doped regimes and the effects of doping and Coulomb interaction on FS are also investigated. Particularly, it is shown that the crossover from hole-like to electron-like FS is deeply affected by the $d-p$ hybridization in the hole-doped case. It has been verified that the effect of the hybridization is very pronounced around the saddle points $(0,\pmπ)$ and $(\pmπ,0)$, where the intensity of the superconducting order parameter is maximum in the particular case of $d_{x^2-y^2}$-wave symmetry. In the electron-doped case, the crossover in the FS is not verified. The doping dependence of the FS topology in the hole- and electron-doped regimes is in agreement with recent experimental ARPES results for La$_{2-x}$Sr$_{x}$CuO$_4$ (hole doping) and Nd$_{2-x}$Ce$_x$CuO$_4$ (electron doping).
The Roth's two-pole approximation has been used by the present authors to investigate the role of $d-p$ hybridization in the superconducting properties of an extended $d-p$ Hubbard model. Superconductivity with singlet $d_{x^2-y^2}$-wave pairing is treated by following Beenen and Edwards formalism. In this work, the Coulomb interaction, the temperature and the superconductivity have been considered in the calculation of some relevant correlation functions present in the Roth's band shift. The behavior of the order parameter associated with temperature, hybridization, Coulomb interaction and the Roth's band shift effects on superconductivity are studied.
The Roth's two-pole approximation has been used by the present authors to study the effects of the hybridization in the superconducting properties of a strongly correlated electron system. The model used is the extended Hubbard model which includes the $d-p$ hybridization, the $p$-band and a narrow $d$-band. The present work is an extension a previous reference [Intern. Journ. of Modern Phys. B, Vol. 18 No. 2 (2004) 241]. Nevertheless, some important correlation functions necessary to estimate the Roth's band shift, are included together with the temperature $T$ and the Coulomb interaction $U$ to describe the superconductivity. The superconducting order parameter of a cuprate system, is obtained following Beenen and Edwards formalism. Here, we investigate in detail the change of the order parameter associated to temperature, Coulomb interaction and Roth's band shift effects on superconductivity. The phase diagram with $T_c$ versus the total occupation numbers $n_T$, shows the difference respect to the previous work.
A theoretical estimate of the explicit time dependence of a drainage water of shallow lakes is presented as an important contribution for understanding the lake dynamics. This information can be obtained from a sum of functions, largely used in fitting of experimental data. These functions were chosen because their centre and weight yield a good description of the water basin behaviour. The coefficients of these functions are here extracted using results of measured and / or calculated data for the state variables describing the shallow West Lake, Hangzou. This procedure can also be applied to other shallow lakes, generating geological information about their drainage basin, which is one of the most important parameters to describe their micrometeorological behaviour. One concludes this work emphasizing the relevance of the explicit time dependence of the drainage variables and the requirement of measured data to validate this approach.