title: Direct observation of dark excitons in individual carbon nanotubes: inhomogeneity in the exchange splitting.
abstract: We report the direct observation of spin-singlet dark excitons in individual single-walled carbon nanotubes through low-temperature micro-magneto-photoluminescence spectroscopy. A magnetic field (B) applied along the tube axis brightened the dark state, leading to the emergence of a new emission peak. The peak rapidly grew in intensity with increasing B at the expense of the originally dominated bright exciton peak and became dominant at B>3 T. This behavior, universally observed for more than 50 tubes of different chiralities, can be quantitatively modeled by incorporating the Aharonov-Bohm effect and intervalley Coulomb mixing. The directly measured dark-bright splitting values were 1-4 meV for tube diameters 1.0-1.3 nm. Scatter in the splitting value emphasizes the role of the local environment surrounding a nanotube in determining its excitonic fine structure.
authors.affiliation: Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Ajit
authors.initials: A
authors.lastname: Srivastava
authors.forename: Han
authors.initials: H
authors.lastname: Htoon
authors.forename: Victor I
authors.initials: VI
authors.lastname: Klimov
authors.forename: Junichiro
authors.initials: J
authors.lastname: Kono