Theory of pseudogaps in charge density waves in application to photo electron or tunneling spectroscopy

TL;DR

This paper models photon absorption in one-dimensional electron-phonon systems with pseudogaps, using nonlinear instanton configurations to predict subgap absorption features observable in spectroscopic experiments.

Contribution

It introduces a theoretical framework for describing subgap absorption in charge density wave systems via nonlinear instanton solutions within the adiabatic approximation.

Findings

Subgap absorption exhibits exponential decay near the free particle edge.

Transition rates follow a power law deep within the pseudogap.

The model applies to systems with gapless modes like 1D semiconductors and incommensurate CDWs.

Abstract

For a one-dimensional electron-phonon system we consider the photon absorption involving electronic excitations within the pseudogap energy range. In the framework of the adiabatic approximation for the electron - phonon interactions these processes are described by nonlinear configurations of an instanton type. We calculate the subgap absorption as it can be observed by means of photo electron or tunneling spectroscopies. In details we consider systems with gapless modes: 1D semiconductors with acoustic phonons and incommensurate charge density waves. We find that below the free particle edge the pseudogap starts with the exponential decrease of transition rates changing to a power law deeply within the pseudogap, near the absolute edge.