Charge-density waves physics revealed by photoconduction

TL;DR

This paper reviews photoconduction studies of Peierls conductors with charge-density waves, highlighting experimental findings, spectral analysis, and a simple energy gap fluctuation model that fits the data well.

Contribution

It provides a comprehensive review of photoconduction in Peierls conductors and introduces a simple model of modulated energy gap consistent with spectral data.

Findings

Fluctuations in the energy gap are surprisingly small, not exceeding a few percent.

Photoconduction effects depend on illumination and electric field, affecting charge transport.

A simple smoothed energy gap model explains the spectral data effectively.

Abstract

The results of photoconduction study of the Peierls conductors are reviewed. The studied materials are quasi-one-dimensional conductors with the charge-density wave: K$_{0.3}$MoO$_3$, both monoclinic and orthorhombic TaS$_3$ and also a semiconducting phase of NbS$_3$ (phase I). Experimental methods, relaxation times, effects of illumination on linear and nonlinear charge transport, the electric-field effect on photoconduction and results of the spectral studies are described. We demonstrate, in particular, that a simple model of modulated energy gap slightly smoothed by fluctuations fits the available spectral data fairly well. The level of the fluctuations is surprisingly small and does not exceed a few percent of the optical energy gap value.