F. López-Aguilar

Molecular EM Fields and Dynamical Responses in Solids with Magnetic Charges

The monopoles are theoretically deflned as charges which produce flelds whose divergence is, obviously, difierent from zero. However, the entities which have been experimentally detected in the spin-ices, with mimetic behavior to that of the magnetic monopoles, generate magnetic flelds which seem to be compatible with r¢B = 0. This apparent contradiction can create confusion and therefore it requires explanation. In this paper we have carried out an analysis of the difierent electromagnetic flelds in the spin- ices materials. We clarify the difierences between the average flelds of standard Maxwell equations with zero divergence even in spin-ices and the non macroscopic flelds when there are magnetic monopoles in these materials. We give the molecular or local flelds which allow us to determine the molecular polarizability. We combine the extended Clausius-Mossotti equations with the Lorentz-Drude model for obtaining the extended susceptibility and the optical conductivity which can be used for explaining the action of the electromagnetic flelds in spin-ices.

Normal state quasiparticle structure in the high-Tc superconductors

Abstract We present a study of the normal state electronic structure of the high- T c superconductors obtained by diagonalizing the one-body Green function of the interacting system. Different approximations to the self-energy are considered. These corrections split the input density of state that is calculated within the local density formalism. The energy-dependent self-energy transfers part of spectral weight to the lower and upper Hubbard peaks, changing also the hole distribution in the different p and d states.

Renormalized electronic structures of CeSi2, CeRu2 and CeAl2

Abstract The renormalized density of states of some Ce compounds is analyzed by considering self-energy effects. We study the influence of the hybridization introduced by the self-energy and how it can affect the shape of the characteristic lower, upper and middle-energy resonance.

Spectroscopic function of the quasiparticles in YBaCuO systems

Abstract An approximation to the self-energy within the so called Green function-W interaction (GW) approximation is used for obtaining the spectrum of quasiparticles of the high Tc superconductors, considered like Hubbard systems with two channels (p and d orbitals) for the localization. In second place, we determine the renormalization factor for each k state which contains hybridized orbitals p and d. The spectral function allows to characterize the quasiparticle states located at an energy interval (± 3 eV) around EF, independently whether they are strongly correlated or not. An important characteristic of the results is the existence of the multiple Hubbard splitting corresponding to the different orbitals p and d of the atoms of the CuO3 linear chain and the CuO2 planes. These splittings lead to the appearence of a gap in the density of states just above the Fermi energy, implying that the superconducting phase is close to other semiconducting one.

Mean-field and beyond mean-field effects on the electronic structure of YBa2Cu3O7

Abstract The electronic structure of YBa 2 Cu 3 O 7 is calculated by means of a method that operates for any self-energy approximation appropriated to strongly correlated systems. Working within the Hubbard picture, we consider mean-field and beyond mean-field approaches with two channels (p and d orbitals) for the localization. The band structure and the renormalized density of states are calculated and compared to available experimental data and theoretical results on YBa 2 Cu 3 O 7 . We find flat bands near the Fermi level, in agreement with angle-resolved photoemission spectra, and dispersion along k z of some bands. Our results show a multiple Hubbard splitting of the different p and d orbitals of the CuO 3 chains and the CuO 2 planes. This splitting leads to a redistribution of the density of holes on the oxygen sites and reasonably agrees with the characteristic disposition of bands of a charge-transfer system.

Hubbard's repulsion, self-energy and quasiparticles: Application to YBa2Cu3O7

Abstract The quasiparticle structure of YBa 2 Cu 3 O 7 is calculated within several approximations to the self-energy (RPA, ERPA, Hubbard I) and the model potential LDA+AMF. The partial DOS and distribution of holes yielded by the different approaches are presented and compared with available experimental data.

Electronic structure of CeSi2

We calculate the electronic structure of CeSi2 using an energy-dependent potential, added to the local density Hamiltonian, arising from an approximation to the self-energy corresponding to a multiband Hubbard Hamiltonian.

Self-Energy Effects in the Electronic Structure of Ce Systems: Application to CeSi2 and CeAl2

We calculate the electronic structure of CeSi2 and CeAl2 using an energy-dependent potential arising from an approximation to the self-energy corresponding to a multiband Hubbard Hamiltonian. This potential is added to the local-density Hamiltonian and we determine the renormalized density of states. This density of states displays different peaks centred about −2.5 eV, ±0.3 eV, and 4 eV with respect to EF, corresponding to the characteristic f features. We analyse these results and compare them with the previous data and theoretical interpretations of the electronic structure of these interesting materials.

LDA+Σ (ω) Method for the Electronic Structure of Strongly Correlated Antiferromagnetic Materials: Application to La2CuO4

In this paper we present a method for obtaining the quasiband structure and the renormalized density of quasistates of strongly correlated systems with antiferromagnetic ordering. We calculate the electronic structure of La 2 CuO 4 in order to test this method. The first step required is to calculate the electronic structure from the local density approximation (LDA) in order to obtain the initial non-interacting ground state. The LDA density of states in strongly correlated systems usually presents serious discrepancies with experimental results. As is well known, these discrepancies, fundamentally concerning photoemission, are due to the fact that the dynamic correlation effects are not taken into account within the LDA. In order to include these effects, we obtain a self-energy potential which allows the initial LDA electronic structure to connect with that of the antiferromagnetic ground state arising from a Bogolyubov-like transformation. Within this new ground state, we determine an antiferromagnetic self-energy by means of a spin density wave procedure, and the interacting Green function yields a density of states which is in reasonable agreement with the experimental photoemission result.

Spin fluctuation effects in normal and s-superconducting states in Hubbard systems

We obtain and discuss the self-energy and the renormalized electronic structure of the normal state in strongly correlated electron systems within the pseudogap regime. The effective potentials considered are found from spin fluctuations within a three-dimensional Hubbard single band model. Vertex effects are included and discussed within this formalism. We find that the self-energy tends to violate the Luttinger theorem when the bandwidths are narrowed. We note that when the bands are further narrowed, the corresponding Eliashberg-like equations tend to yield superconductivity.