Unconventional charge density wave driven by electron-phonon coupling

TL;DR

This paper introduces a new mechanism for unconventional charge density waves driven by momentum-dependent electron-phonon interactions in quasi-one-dimensional conductors, revealing unique optical and collective properties.

Contribution

It proposes a novel electron-phonon coupling mechanism for UCDWs and analyzes their excitation spectrum, optical conductivity, and effective mass using mean field theory.

Findings

Fluctuations cause the UCDW to slide as a whole.

Optical conductivity is significantly affected by collective modes.

Effective mass varies nonmonotonically with temperature.

Abstract

We report our study on unconventional charge density waves (UCDW) (i.e. a charge density wave with wavevector dependent gap) in pure quasi-one dimensional conductors. We develop a new 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 q and the momentum of the scattered electron 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.