Superconductivity and Martensitic Transformations in A-15 Compounds

Abstract

I would like to discuss the current theories of the martensitic transition in A15 compounds and our understanding of the interplay between the martensitic transition and superconductivity. Labbe and Friedel 1/ proposed that the martensitic transition is driven by an electronic band Jahn-Teller effect. Gorkov 2,3/ proposed an alternative model in which the martensitic transition is driven by the Peierls mechanism of an energy gap opening up near the Fermi energy. Both models are based on one-dimensional or quasi-one-dimensional energy band models which are inconsistent with APW band calculations. 4/ Bhatt 5/ has developed a very successful Landau theory which is based on the Gorkov model and which is, of course, free of any microscopic assumptions about the nature of the band structure. Bhatt 6/ has also developed a microscopic theory using a band structure model based on the APW band structure. This model includes both the band Jahn-Teller effect and the Peierls effect and is therefore a synthesis of the Labbe-Friedel and Gorkov models. The effects on superconductivity are illustrated in a calculation by Bilbro, 7/ based on the Gorkov model, in which both a Peierls energy gap and the BCS energy gap are included in the theory.