Energy bands in the bismuth structure. I. A nonellipsoidal model for electrons in Bi

The band structure near a minimum at a point of no special symmetry is examined for energies small compared to all band gaps except that to the next lower band. Spin-orbit coupling is included. The theory is specialized to points having the three possible symmetries of electrons in Bi and further simplifications appropriate to Bi made. The resulting nonellipsoidal energy surfaces are studied in some detail. An experiment is suggested which is capable of distinguishing between the three possibilities. Fitting the model to existing information is not carried out in this paper.