[en] Exact localised ground-states are presented for the one- and two-dimensional periodic Anderson model at finite U > 0 in restricted regions of the parameter space, which extends from the low U to the high U regions as well. The physical properties of this phase are analysed in detail. (author)

[en] The phase diagram of the antiferromagnetic superconductor is calculated in a model with two parallel pieces of the Fermi surface and near the critical temperature of the antiferromagnetic state. (orig.)

[en] On the basis of the Anderson lattice description and taking into account a two-particle hybridization term, the coexistence between the mixed valance and weak coupling superconducting properties in Ce-rich rare earth intermetallic compounds is analyzed. The theoretical results can be used for the interpretaiton of the experimental data measured in CeRu₃Si ₂

[en] A simple superconducting model for heavy Fermion systems is studied taking into account an antiparallel intersite coupling between the f electrons, which may have superexchange nature. Some characteristics of the model is analysed and the 1/T₁ relaxation rate measurement for CeCu₂Si₂ is explained. (author)

[en] The short-range interaction between magnetic impurities is considered in order to explain the coexistence between superconductivity and the spin-glass state. Specific heat calculations in different temperature regions show good agreement with the experimental data

[en] The deviation of the superconducting transition temperature from the Abrikosov-Gorkov behavior in the case of La/sub 1-x/Gd/sub x/ is explained considering the presence of short range spin-glass at low temperature. The theoretical results show good agreement with the experimental data

[en] The interplay of superconductivity and spin-density waves in a two-band system with imperfect nesting and interband coupling is analyzed. Within this model, enhancement of the superconducting critical transition temperature is found. The influence of the interband coupling on this enhancement is presented in detail. The possible connections with the high-T/sub c/ oxidic systems are also discussed. The obtained curves of T/sub c/ versus the excess carrier concentration fit well with both La-Ba-Cu-O and Y-Ba-Cu-O cases

[en] The original Cooper pairing theory is reformulated for electrons confined in a layer. This analysis is motivated by the quasi-two-dimensional character of the oxidic superconductors, in case of which the extension of the initial (3D) Cooper framework is practically impossible. By considering the electrons moving in a flat box, due to quantum size effect the properties of these oxidic superconductors can be explained in a natural way. In this paper, the authors concentrate to the variation of the critical transition temperature due to the layer thickness and to the number of conduction (Cu-O) planes. The results are confirmed by the experiment

[en] This paper describes different superconducting phases in layered systems, by taking into account in- and inter-layer couplings. The effect of in-layer magnetic and nonmagnetic impurities on these phases are discussed. The possible interferences with high T_c materials is also analyzed

[en] The coexistence of spin-density waves and superconductivity has been theoretically analyzed in a two-band model, a case for which the commonly used descriptions for the ternary rare-earth compounds and highly anisotropic organic solids are unapplicable. The phase diagram at T = 0, the temperature dependence of the order parameters, and the critical transition temperatures have been obtained. The theoretical results are in good agreement with the experiments concerning the Cr alloys