Sommaire:

Since the first experimental evidence of photoluminescence of semiconducting single-walled carbon nanotubes (SWNTs), 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 experimental investigation of the intrinsic optical properties of SWNTs is challenging since they are extremely sensitive to the influence of their physico-chemical environment. In this context, samples with reduced perturbations, such as suspended SWNTs, are particularly interesting.
In this talk, I will present an experimental study of the magneto-optical properties of suspended SWNTs through time-resolved photoluminescence spectroscopy. Measurements are performed at the single-object level using a home-built confocal optical microscope with a large numerical aperture (NA = 0.95) operating at cryogenic temperature (down to 2K) and high magnetic field (up to 7T). The evolution of the photoluminescence spectra and decay signals with increasing magnetic fields shows the influence of the Aharonov-Bohm effect on the two lowest-energy singlet excitons, namely the ground exciton which is optically inactive (dark exciton) and an exciton lying a few millielectronvolts higher in energy which is optically active (bright exciton). A model based on rate equations and including the Aharonov-Bohm coupling between these two excitons enables to determine separately the excitons lifetimes and to derive quantitative information on the energy relaxation from the photo-excited higher levels. The energy relaxation following the photo-excitation of the S22 transition leads to a bright state population efficiency four times lower than that of the dark state, but it significantly increases when energy relaxation occurs from the KK’ excitonic levels. Thanks to a good signal to noise ratio, the photoluminescence spectra also reveal the presence of a very weak intrinsic zero-field coupling between the dark and the bright excitons, as well as an excitonic mobility preserved at liquid helium temperature in suspended SWNTs.

Pour plus d'informations, merci de contacter Jacques V.