O.L.T. de Menezes

Importance of hybrid pairs in superconductors

Abstract The role of hybrid pairs in a system of two hybridized bands in the presence of electron-phonon interaction is studied. In the superconducting regime we can obtain a general gap equation for the Cooper pairs as function of the hybridization and of the ratio between the bandwidths. The importance of the interband pairs compared to the intraband pairs is discussed.

Hyperfine field systematics of s-p impurities in Gd

Abstract A model, which is an extension on that of Daniel and Friedel, is adapted to describe the hyperfine fields on s-p impurities in Gd. The model allows the description of two kinds of behaviour of the sign of the hyperfine field when one goes from the beginning to the end of an s-p series, namely, a negative sign and, a change of sign.

Valence instability and electron-phonon interaction in SmS

Abstract It is proposed a simple model which describes the discontinuous phase transition and valence instability in SmS. It differs from other models in that, the instability due to increasing applied pressure, is completely described in terms of the semiconducting phase without using characteristics of the metallic phase. The electron-phonon interaction which renormalizes the pure electronic f ⇆ d hybridization generates the occurence of such behavior. It is shown that above a ratio, between electron-phonon coupling and pure electronic f ⇆ d mixing, the semiconductor-metal transition is displayed.

On the valence and lattice parameter in cerium intermetallic compounds

Abstract Experimental data concerning valence and lattice parameter in cerium intermetallic compounds are discussed using the concepts of electronic charge screening and charge transfer between the rare earth and the transition element.

An analysis of the ESR-linewidth results in intermediate valence systems Ce(Pd3-xTx) (T = Rh, Ag)

Abstract We study the deviation from the linear Korringa relaxation behavior using a previously suggested model. An analytical expression for the ESR-linewidth dependence with the temperature is applied to the intermediate valence pseudo-binary compounds Ce(Pd 3- x T x ) ( T = Rh , Ag). We discuss our results and compare them to those obtained by other models.

On the stability of interband pairs in superconductors

Abstract We consider the presence of interband pairs in two-band superconductors. The stabilization singlet and triplet states are analysed in terms of the type of interactions, which could be responsible for the superconducting behaviour. The general case involving only interband pairs is considered and comparations with previous suggestions on the hybrid pairs in heavy fermion systems are discussed.

Evaluation of the 4ƒ-level width from ESR in Ce(A1−xBx)n

Abstract We consider a model that describes the temperature dependence of the Gd-ESR linewidth in intermediate valence pseudo-binary compounds like Ce(A 1− x B x ) n ( n = 2, 3). The set of x -dependent Δ H vs T curves is in qualitative agreement with the experimentally observed shapes. For CePd 3 , one evaluates the 4 f -level width, its position and the “normal” relaxation parameter.

On the temperature dependence of the EST linewidth in CexLa1−xOs2

Abstract We study a model to describe the non-linear behaviour of the Gd ESR linewidth with temperature in CexLa1−xOs2. The model is based on the change of the local density of states due to the variation of the Gd neighbourhood with x and can account qualitatively for the observed results.

RETRIEVAL IN INTERACTING NEURAL NETWORKS

We study the associative memory properties for a particular structure of neural network. It is assumed a low connectivity between two highly connected network regions. As process of common learning correlates the subpatterns stored in each region. The retrieval of the global pattern is studied as a function of the overlap between the associated subpatterns.

Large 2ΔkBTc values in two band superconductors

Abstract The observation of anomalous 2Δ/ k B T c ratios, above the BCS value, has been understood as an evidence of the strong coupling limit. We show that for two interacting band states, in the superconducting regime, large values of these ratios can be expected for small values of λ, the effective electron-electron coupling.