Electron orderings and distortions in quasi-one-dimensional systems with a half-filled band

Abstract

A model for description of electron orderings and lattice distortions in quasi-one-dimensional half-filled band systems involving intra- and interchain electron interactions and electron-lattice couplings is considered. Its thermodynamic properties are analysed both within the broken symmetry H-F approximation and within the degenerate perturbation theory for the strong intra-atomic interaction limit, and stability conditions for various possible types of orderings are determined. Antiferromagnetism (AF) and site charge ordering (C1) are found to exclude one another whereas dimerization accompanied by bond charge ordering can coexist with AF and C1 in the limited range of parameters diminished by hopping and electron-photon coupling via Coulomb forces. Nearest-neighbour Coulomb interactions stabilize C1 but they can also essentially enhance transition temperatures and energy gaps in dimerized phases and suppress the corresponding quantities in AF phases. The effects of long-range electron interactions and the electron-phonon coupling via Coulomb forces are also discussed.