Unconventional charge-density waves driven by electron-phonon coupling

Abstract

We report our study on unconventional charge-density waves (UCDW) (i.e., a charge-density wave with a wave vector dependent gap) in pure quasi-one-dimensional conductors. We develop a possible mechanism of establishment of such a low temperature phase, in which the driving force of the phase transition is the electron-phonon interaction with coupling depending on both the momentum transfer $(\mathbf{q})$ and the momentum of the scattered electron $(\mathbf{k})$. Mean field treatment is applied to obtain the excitation spectrum, correlation functions such as the density correlator and the optical conductivity, and the effective mass of the phase excitation. The fluctuation of the order parameter leads to the sliding of the UCDW as a whole. In the absence of impurities, we calculated the effect of this fluctuation on the optical properties. The inclusion of the collective mode significantly alters the optical conductivity, and leads to an effective mass which is nonmonotonic in temperature as opposed to conventional CDWs.