title: Exciton-plasmon States in nanoscale materials: breakdown of the Tamm-Dancoff approximation.
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.
authors.affiliation: European Theoretical Spectroscopy Facility, Université Catholique de Louvain, Belgium. myrta@teor.fis.uc.pt
authors.forename: Myrta
authors.initials: M
authors.lastname: Grüning
authors.forename: Andrea
authors.initials: A
authors.lastname: Marini
authors.forename: Xavier
authors.initials: X
authors.lastname: Gonze