Invited Presentation: Unifying the Low Temperature Luminescence Spectra of Carbon Nanotubes

Photo-excited electron-hole pairs in carbon nanotubes form strongly bound and localized excitons that can recombine radiatively giving rise to near infrared luminescence signals. Due to the coupling to acoustic phonons, this PL line was predicted to be strongly broadened (even at low temperature), leading to asymmetrical meV-broad phonon sidebands. In addition, due to the peculiar one-dimensional geometry, the (possibly narrow) zero phonon line (ZPL) is completely merged into the phonon wings resulting in an overall broad and asymmetric PL line [1]. This picture was recently puzzled by the observation of ultra narrow PL lines in suspended nanotubes [2,3] raising questions about the electron-phonon coupling mechanisms. Here, we show that ultra narrow PL lines can also be observed for regular micelle wrapped nanotubes deposited on a substrate. However, a high resolution measurement allows to identify attenuated sidebands that are reminiscent of the one-dimensional electron-phonon coupling. This observation allows to interpret both the narrow and the broad lines in terms of modified electron-phonon coupling in a unified framework [4]. [1] Galland et al. PRL 101, 067402 (2008) [2] Hofmann et al., Nature nano. 8, 502 (2013) [3] Sarpkaya et al., Nature comm. 4, 2152 (2013) [4] Vialla et al., submitted