Survey of exciton-phonon sidebands by magneto-optical spectroscopy using highly specified (6,5) single-walled carbon nanotubes

Abstract

We report the first high-field magneto-optical study on the exciton-phonon sideband of single-walled carbon nanotubes (SWNTs) consisting only of (6,5) species. Both energy and intensity of the observed phonon sideband were found to be independent of the external magnetic field. Comparing with theoretical calculations, we confirmed that these sidebands originate from the optically forbidden K-momentum singlet excitons. Energy of these K-momentum dark excitons was extracted to be ~ 21.5 meV above the bright Γ-momentum singlet excitons, in close agreement with recent theoretical predictions and experimentally determined values.

Exciton-phonon bound complex in single-walled carbon nanotubes revealed by high-field magneto-optical spectroscopy

“…Thus, the distinctive evolution of SWNT excitonic states in external magnetic fields, which is wellknown as a manifestation of the Aharonov-Bohm (AB) effect [11][12][13][14][15][16][17][18], serves as an efficient tool to clarify the origin of phonon sidebands. In the following, we would show that both energy and intensity of the E 22 phonon sideband are immune to the external magnetic field, the same as its E 11 counterpart [8]. However, unlike conventional absorption measurements, the absorption intensity of E 22 phonon sideband is as low as ∼ 0.019 O.D.…”

“…The unique one-dimensional sp 2 -bonded carbon structure of SWNTs leads to exceptionally large excitonic effect as well as enhanced exciton-phonon interaction. Such exciton-phonon bound complexes were predicted theoretically and observed experimentally by means of various spectroscopic techniques, such as photoluminescence, photoluminescence excitation and optical absorption measurements [1][2][3][4][5][6][7][8]. However, it is only recently that these phonon sidebands were confirmed to originate from the dark K-momentum singlet (D-K-S) exciton |KK ′ &K ′ K >, among the complicated excitonic structures of SWNTs that comprise a total of 16 excitonic states.…”

“…To clarify these issues, we perform precise high-field magneto-optical measurements on the E 22 vibronic sideband of the (6,5) species. The reason to choose the (6,5) species is that, this species has been demonstrated in our previous work to show subband dependence for the relative ordering between B-Γ-S and D-Γ-S excitons [9], and their E 11 phonon sideband has been confirmed to originate from the D-K-S exciton [7,8]. It is thus convenient to explore the robustness of the D-K-S excitonic level and the possibility of sub-band dependence for the phonon sideband origin by studying the E 22 manifold and comparing with the well-established E 11 results.…”

“…However, it is only recently that these phonon sidebands were confirmed to originate from the dark K-momentum singlet (D-K-S) exciton |KK ′ &K ′ K >, among the complicated excitonic structures of SWNTs that comprise a total of 16 excitonic states. [7,8].…”

“…For magnetoabsorption measurements, the pulsed magnetic field was generated by a wire-wound solenoid coil with a maximum field of ∼ 52 T. Both the incident and transmitted light from a pulsed halogen lamp was guided by optical fibers and finally detected by an electrically cooled ICCD. Spectra were taken on the top of the pulsed field with an exposure time of 5 ms under the Voigt geometry [8].…”