The energy band model for bismuth: Resolution of a theoretical discrepancy

The Lax two-band model contains a term linear in wave vector which is missing in the Abrikosov-Falkovsky model. It is shown that this term is recovered if the Abrikosov-Falkovsky development is carried to second order. It is argued from the results of energy band calculations and from experiment that the term in question is as important as the term second order in wave vector which was introduced by Cohen and by Abrikosov and Falkovsky. From a study of cyclotron resonance and de Haas-van Alphen effect it is concluded which second-order terms in the general Cohen model must be kept in order to obtain agreement with experiment.