Optical signatures of exciton-polarons from diagrammatic Monte Carlo

TL;DR

This paper uses diagrammatic Monte Carlo to analyze how electron-electron and electron-phonon interactions influence exciton formation and optical responses in solid-state systems, revealing phonon cloud effects and differences between adiabatic regimes.

Contribution

It introduces an approximation-free Monte Carlo approach to study optical signatures of exciton-polarons across various interaction regimes.

Findings

Excitons become dressed by phonons with increasing electron-phonon coupling.

Significant differences are observed between adiabatic and anti-adiabatic regimes.

The method provides detailed spectral functions for correlated electron-phonon systems.

Abstract

We study the interplay of electron-electron and electron-phonon interactions in the course of electron-hole bound state formation for gapped solid state systems. Adapting the essentially approximation-free diagrammatic Monte Carlo method for the calculation of the optical response, we discuss the absorption of light in correlated electron-phonon systems for the whole interaction and phonon frequency regimes. The spectral function obtained by analytical continuation from the imaginary-time current-current correlation function demonstrates the dressing of excitons by a phonon cloud when the coupling the lattice degrees of freedom becomes increasingly important, where notable differences show up between the adiabatic and anti-adiabatic cases.