Translation-Invariant Excitons in a Phonon Field

TL;DR

This paper investigates translation-invariant excitons in polar crystals, revealing how phonon interactions influence their ground state energy and spectral properties, especially under varying electron-phonon coupling strengths.

Contribution

It introduces a translation-invariant framework for excitons interacting with phonons, clarifying conditions for their energy contributions and spectral behavior across coupling regimes.

Findings

Phonons contribute to exciton ground state energy only at weak or intermediate coupling.

Self-trapped excitons are not possible in strong coupling regimes.

The hydrogen-like exciton model remains valid under certain electron-phonon interaction conditions.

Abstract

Large-radius excitons in polar crystals are considered. It is shown that translation invariant description of excitons interacting with a phonon field leads to a nonzero contribution of phonons into the exciton ground state energy only in the case of weak or intermediate electron-phonon coupling. A conclusion is made that self-trapped excitons cannot exist in the limit of strong coupling. Peculiarities of the absorption and emission spectra of translation invariant excitons in a phonon field are discussed. Conditions when the hydrogen-like exciton model remains valid in the case of electron-phonon interaction are found.