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Exciton-plasmon states in nanoscale materials: breakdown of the Tamm-Dancoff approximation

Authors: M. Grüning, A. Marini, X. Gonze

Ref.: Nano Letters 9, 2820-2824 (2009)

Abstract: Within the Tamm−Dancoff approximation, ab initio approaches describe excitons as packets of electron−hole pairs propagating only forward in time. However, we show that in nanoscale materials excitons and plasmons hybridize, creating exciton-plasmon states where the electron−hole pairs oscillate back and forth in time. Then, as exemplified by the trans-azobenzene molecule and the carbon nanotubes, the Tamm−Dancoff approximation yields errors larger than the accuracy claimed in ab initio calculations. Instead, we propose a general and efficient approach that avoids the Tamm−Dancoff approximation, correctly describes excitons, plasmons, and exciton-plasmon states, and provides a good agreement with experimental results.

DOI: 10.1021/nl803717g