Anomalous strong exchange narrowing in excitonic systems

TL;DR

This paper theoretically studies exchange narrowing in excitonic chains, revealing a strong 1/N narrowing effect in non-Markovian environments, contrasting with the absence of narrowing in Markovian cases.

Contribution

It demonstrates a novel 1/N exchange narrowing effect in non-Markovian environments, differing from traditional 1/√N results, and analyzes various spectral width measures.

Findings

In non-Markovian environments, peak width narrows by a factor of 1/N.

No exchange narrowing occurs in Markovian environments.

Different spectral width measures show consistent narrowing behavior.

Abstract

We investigate theoretically the phenomenon of exchange narrowing in the absorption spectrum of a chain of monomers, which are coupled via resonant dipole-dipole interaction. The individual (uncoupled) monomers exhibit a broad absorption line shape due to the coupling to an environment consisting of a continuum of vibrational modes. Upon increasing the interaction between the monomers, the absorption spectrum of the chain narrows. For a non-Markovian environment with a Lorentzian spectral density, we find a narrowing of the peak width (full width at half maximum (FWHM)) by a factor 1/N, where N is the number of monomers. This is much stronger than the usual 1/sqrt{N} narrowing. Furthermore it turns out that for a Markovian environment no exchange narrowing at all occurs. The relation of different measures of the width (FWHM, standard deviation) is discussed.