Insulator-metal transition versus temperature for the CDW of the 1D adiabatic Holstein model

Abstract

We perform a numerical study of the classical atomic configuration which minimizes the electronic free energy at finite temperature of the 1D adiabatic Holstein model. For a fixed incommensurability, the ground-states which are insulating bipolaronic incommensurate charge density wave (CDW) may undergo a second-order transition into a conducting Peierls-Fröhlich CDW when the temperature increases (inverse transition by breaking of analyticity). The global phase diagram is calculated as a function of temperature and electronic chemical potential μ. When increasing the temperature, the high commensurability and incommensurate CDWs progressively disappear. The same phase diagram represented as a function of temperature and electronic band filling exhibits phase separations between different commensurate structures also involving charge separations (which are physically unacceptable). Thus it is demonstrated that at moderate electron-phonon couplings which are in the range of those of real systems, the standard mean field theory of CDW is inconsistent with the real behaviour of the model.