Commensurate-Incommensurate Phase Transition in Nearly Half-Filled Band

Abstract

The phase diagram and the character of the commensurate-incommensurate (C-IC) phase transition are discussed for the one-dimensional electron phonon system with the nearly half-filled band in a mean field approximation which includes the relevant higher harmonics. In the case of the infinite reservoir we find that the C-IC phase transition is of first order and that the commensurate phase is convex on the (µ, T) plane, where µ is the Fermi energy as measured from the middle of a condition band. In the case of the finite reservoir the slope of TCI(µ) (the C-IC transition temperature) line at the triple point is calculated analytically by assuming only one condensed phonon in the IC-state.