Some comments on the excitonic mechanism of superconductivity

The Inkson and Anderson (IA) objection to the calculation of Allender, Bray and Bardeen (ABB) is investigated. The IA model dielectric functions are compared with the Lindhard and band structure dielectric functions; the consequences of the use of these dielectric functions is discussed. It is also demonstrated that a dielectric function calculated for Ge gives a repulsive superconductivity kernel for all frequencies. The relation of this result to the calculation of ABB and the role of local-fields or umklapp processes is discussed