Metallic ions, effect superconductivity

The exciting discovery of super-conductivity in metallic fiillerencs (f) leads us to inquire whether the classic mechanism for superconductivity, namely, effective electron-electron attraction via the interaction of electrons with vibrations of the ions, is applicable here as well. Associated with this is the question of whether the direct electron-electron repulsion in FuUerenes can suppress conventional singlet pairing. In this paper we exploit the special nature of cluster compounds to derive a particularly simple expression for electron-vibrational coupling from which parameters of the superconducting state of fuUerenes are easily calculated. Further, we present arguments why the effective repulsions in fuUerenes are no different than in conventional metals. 

The interaction between impurity ions with partially filled d or f electron shells and the conduction electrons of a metallic host can lead to variations in certain physical properties with temperature and magnetic field which have come to be associated with the Kondo effect . In zero magnetic field, these temperature-dependent anomalies in the physical properties scale with a characteristic temperature Tk, the so-called Kondo temperature, above which the matrix-impurity system behaves magnetically and below which the matrix-impurity system behaves nonmagnetically. The physical properties which exhibit anomalies attributable to the Kondo effect include the electrical resistivity, magnetic susceptibility, thermoelectric power, specific heat and, in systems where appropriate, superconducting properties such as the critical temperature and the jump in specific heat which occurs at T. ... 

In this chapter we have shown how critical the local structure is to the elucidation of the properties of mixed-ion oxides such as the CMR manganites, ferroelectric titanates, and superconducting cuprates. The effect of local structure is more pronounced for oxides than for free-electron metals since the local structure tends to be better defined in oxides due to their covalent bonding, relatively open structure, and the tendency for charge localization. In metals, on the other hand, small local effects are smeared out because of delocalized charge, strong screening, and densely packed structure. 

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