Dresden 2011 – scientific programme

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MO: Fachverband Molekülphysik

MO 11: Poster: Transport and Spectroscopy in Molecular Nanostructures (Intersectional Session with CPP)

MO 11.3: Poster

Tuesday, March 15, 2011, 18:00–20:00, P1

Anomalous strong exchange narrowing in excitonic systems — •Jan Roden and Alexander Eisfeld — MPI-PKS Dresden

Whenever electronic transitions interact with an environment, i.e. they are affected by static or dynamic disorder, the absorption lines are broadened. However, if several of those electronic (two-level) systems are coupled so that they exchange excitation, the absorption spectrum can be strongly narrowed compared to the absorption of the uncoupled systems. This remarkable phenomenon, the so-called exchange narrowing, has been observed already several decades ago in the absorption spectra of molecular aggregates – it is responsible for the narrow shape of the well-known J-band of organic dye aggregates (J-aggregates).

Often the number of coherently coupled monomers is estimated from the narrowing of the spectrum. Usually it is assumed that the narrowing is given by a factor 1/√N (where N is the number of the coupled monomers) that is obtained e.g. for uncorrelated Gaussian static disorder.

Here we consider dynamic disorder and find, using numerical quantum calculations, for a non-Markovian environment a strongly enhanced narrowing of a factor 1/N. On the other hand, for a Markovian environment it turns out that no narrowing at all occurs, showing that the narrowing strongly depends on the model assumed.