High-field magnetooptical behavior of polymer-embedded single-walled carbon nanotubes

We report a study of the magnetophotoluminescence (PL) of single-walled carbon nanotubes embedded in polymer films. The magnetic-field dependence of the intensity and emission energy is used to deduce the splitting and mixing of the bright and dark exciton states. It is shown that the presence of strain in the films causes a considerable increase in the bright-dark exciton splitting. The unstrained nanotubes show considerably smaller exciton splittings than reported previously and demonstrate an unexpected magnetic suppression of the PL intensity which can only be observed once the Aharanov-Bohm phase splitting is significantly larger than the bright-dark exciton splitting. Functional fitting of the data also allows the diameter dependence of the Aharanov-Bohm (AB) phase-induced energy shifts to be accurately measured. Evidence is also presented for the existence of a zero-field AB splitting due possibly to spin-orbit interaction effects.