Infrared conductivity of a one-dimensional charge-ordered state: quantum lattice effects

TL;DR

This paper investigates the infrared optical properties of a one-dimensional charge-ordered state in the Holstein model, highlighting the effects of lattice fluctuations and electron-phonon interactions on the conductivity spectrum.

Contribution

It introduces an improved variational approach that includes second-order lattice fluctuations to analyze the optical conductivity in the charge-ordered phase.

Findings

Lattice fluctuations create a subgap tail in infrared conductivity.

Electron-phonon interactions broaden the optical gap.

Results align well with experimental spectra.

Abstract

The optical properties of the charge-ordering ($CO$) phase of the one-dimensional (1D) half-filled spinless Holstein model are derived at zero temperature within a well-known variational approach improved including second-order lattice fluctuations. Within the $CO$ phase, the static lattice distortions give rise to the optical interband gap, that broadens as the strength of the electron-phonon ($el-ph$) interaction increases. The lattice fluctuation effects induce a long subgap tail in the infrared conductivity and a wide band above the gap energy. The first term is due to the multi-phonon emission by the charge carriers, the second to the interband transitions accompanied by the multi-phonon scattering. The results show a good agreement with experimental spectra.