Screening is limited in single-walled carbon nanotubes because of their one-dimensional nature, and the strong Coulomb interactions result in optical spectra dominated by excitons with binding energies lager than half an eV. Also because of the limited screening, a charged carrier can be bound to an exciton to form a trion that is stable at room temperature.

Here we discuss experiments aimed at highlighting the behaviors of excitons and trions under electric fields. Microspectroscopy measurements are performed on individual suspended carbon nanotubes integrated into field-effect devices. Simultaneous photoluminescence and photoconductivity spectroscopy show evidences for spontaneous dissociation [1], despite the expectation that free carrier generation from such a tightly-bound state would be difficult. As the field is increased, we observe an emergence of new absorption peaks in the excitation spectra, which can be explained by electrical activation of dark excited states [2]. Although trion formation has been thought to be difficult in suspended nanotubes due to low exciton-carrier scattering rates, we have succeeded in identifying trion emission under an application of gate voltages [3].

Work supported by KAKENHI, The Canon Foundation, The Asahi Glass Foundation, and the Photon Frontier Network Program of MEXT, Japan.

[1] Y. Kumamoto, M. Yoshida, A. Ishii, A. Yokoyama, T. Shimada, Y. K. Kato, Phys. Rev. Lett. 112, 117401 (2014).
[2] T. Uda, M. Yoshida, A. Ishii, Y. K. Kato, submitted.
[3] M. Yoshida, A. Popert, Y. K. Kato, arXiv:1510.08996.