Magneto-photoluminescence spectroscopy of bright and dark excitons in suspended semiconducting single-walled carbon nanotubes

Morgane Gandil 1 Kazunari Matsuda 2 Philippe Tamarat 1 Brahim Lounis 1
1 lp2n-01,lp2n-12
LP2N - Laboratoire Photonique, Numérique et Nanosciences
Abstract : Since the first experimental evidence of photoluminescence (PL) of semiconducting single-walled carbon nanotubes (SWNTs) [1], studies have been conducted to investigate the optical properties of these nano-structures, motivated by possible applications in the fields of quantum information, biological labeling, opto-electronics or laser technology. The unidimensional nature of SWNTs, through the combined effect of strong spatial confinement and low coulomb screening, leads to high electron-hole binding energies [1,2]. Therefore, the photo-excitation of SWNTs results in the formation of strongly correlated electron-hole pairs, so-called excitons, which dominate their photo-physical behavior. Due to the configuration of the excitonic band structure, the luminescence of semiconducting SWNTs is mainly governed by the two lowest singlet states: the upper one is optically active (bright) whereas the lower one corresponds to a parity forbidden dipole transition (dark). A magnetic field applied along the SWNT axis induces the coupling of these two levels through the Aharonov-Bohm effect. The resultant magnetic brightening of the dark state, illustrated in the figure, opened up the field of magneto-photoluminescence spectroscopy [3] as a promising way to investigate the photo-physical properties of SWNTs. Here, we report the study of isolated CVD-grown SWNTs suspended on lithographed trenches of a silicon substrate. Measurements were performed at the single-object level using a home-built confocal optical microscope with a large numerical aperture (NA = 0.95) operating at cryogenic temperatures (down to 2K) and high magnetic field (up to 7T). PL spectra and PL decay signals of single isolated SWNTs were acquired under various experimental conditions, including different magnetic fields and optical excitation frequencies. We developed a two level model based on the dark and bright excitons, which explains the experimental results in both spectral and time domains. Thanks to the complementarity of PL spectra end PL decay signals, we were able to retrieve quantitative information on the energy relaxation dynamics that follow the photo-excitation of SWNTs. In particular, we found that the branching ratio from S22 or KK' states strongly favors the formation of the dark exciton (≈90% and ≈80% respectively). This result, in contrast with the common hypothesis of an initially dominant bright population, is consistent with a recent Terahertz experiment [4].
Type de document :
Communication dans un congrès
Annual Meeting of the GDR-I Graphene Nanotubes, Oct 2016, Saint Pierre d'Oléron, France. 2016
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Soumis le : lundi 20 novembre 2017 - 15:01:37
Dernière modification le : jeudi 11 janvier 2018 - 06:26:24

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  • HAL Id : hal-01636717, version 1

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Morgane Gandil, Kazunari Matsuda, Philippe Tamarat, Brahim Lounis. Magneto-photoluminescence spectroscopy of bright and dark excitons in suspended semiconducting single-walled carbon nanotubes. Annual Meeting of the GDR-I Graphene Nanotubes, Oct 2016, Saint Pierre d'Oléron, France. 2016. 〈hal-01636717〉

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