Dispersion of incoherent spectral features in systems with strong electron-phonon coupling

TL;DR

This paper develops a simple adiabatic approximation method to analyze how strong electron-phonon coupling affects spectral features in doped systems, explaining spectral broadening without dispersion change, consistent with ARPES data on undoped cuprates.

Contribution

It introduces an adiabatic approximation approach for calculating spectra in systems with strong electron-phonon coupling, especially when initial states are unaffected by this coupling.

Findings

Spectra are broadened by electron-phonon coupling without changing dispersion.

The method explains ARPES observations in undoped cuprates.

Strong initial-state electron-phonon coupling alters spectral relations.

Abstract

We study (inverse) photoemission from systems with strong coupling of doped carriers to phonons. Using an adiabatic approximation, we develop a method for calculating spectra. This method is particularly simple for systems where the electron-phonon coupling can be neglected in the initial state, e.g., the undoped t-J model. The theory then naturally explains why the electron-phonon coupling just leads to a broadening of spectra calculated without electron-phonon coupling, without changing the dispersion. This is in agreement with recent angle-resolved photoemission spectroscopy (ARPES) on undoped cuprates, and it supports the interpretation in terms of strong electron-phonon interaction. The theory also shows that for systems with strong electron-phonon coupling in the initial state, the result cannot in general be related to the spectrum obtained without electron-phonon coupling.