Studies of the structural stability of an electronic system with a two-fold degenerate band

Abstract

A general expression has been derived for the change of free energy of a partially filled two-fold degenerate band due to the electron-phonon coupling, taking into account the splitting of the $e_g$ density of states by the axial crystal field produced by the lattice distortion. Analogous to the Stoner's theory of itinerant ferromagnets, an analytical expression for the martensitic transition temperature $T_M$ has been obtained in the limit of $k{T}_M\ll B$, the bandwidth. The problem of the phase stability has then been studied numerically. Implications of these results are discussed in the background of available experimental results.