Demons and superconductivity

Model calculations are used to explore the role of demons (acoustic plasmons involving light and heavy mass carriers) in superconductivity. Heavy $d$ electrons and light $s$ and $p$ electrons in a transition metal are used for discussion, but the calculation presented is more general, and the results can be applied to other systems. The analysis is based on the dielectric-function approach and the Bardeen-Cooper-Schrieffer theory. The dielectric function includes intraband and interband $s-d$ scattering, and a tight-binding model is used to examine the role of $s-d$ hybridization. The demon contribution generally reduces the Coulomb interaction between the electrons. Under suitable conditions, the model calculations indicate that the electron-electron interaction via demons can be attractive, but the results also suggest that this mechanism is probably not dominant in transition metals and transition-metal compounds. An attractive interband contribution is found, and it is proposed that this effect may lead to pairing in suitable systems.