Optical conductivity of the Holstein polaron

TL;DR

This paper introduces a new analytical approach to compute the optical conductivity of Holstein polarons, linking it to phonon cloud structure, applicable in any dimension, and validated against numerical results.

Contribution

It presents a novel non-perturbational analytical expression for Holstein polaron optical conductivity that is versatile and systematically improvable.

Findings

Accurate analytical expression for OC of Holstein polarons.

Method works in any dimension and with momentum-dependent couplings.

Validated against diagrammatic Monte Carlo results.

Abstract

The Momentum Average approximation is used to derive a new kind of non-perturbational analytical expression for the optical conductivity (OC) of a Holstein polaron at zero temperature. This provides insight into the shape of the OC, by linking it to the structure of the polaron's phonon cloud. Our method works in any dimension, properly enforces selection rules, can be systematically improved, and also generalizes to momentum-dependent couplings. Its accuracy is demonstrated by a comparison with the first detailed set of three-dimensional numerical OC results, obtained using the approximation-free diagrammatic Monte Carlo method.