Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon Nanotubes

Abstract

Optical properties of single-wall carbon nanotubes (SWCNTs) for light polarized parallel to the nanotube axis have been extensively studied, whereas their response to light polarized perpendicular to the nanotube axis has not been well explored. Here, by using a macroscopic film of highly aligned single-chirality (6,5) SWCNTs, we performed a systematic polarization-dependent optical absorption spectroscopy study. In addition to the commonly observed angular-momentum-conserving interband absorption of parallel-polarized light, which generates $E_{11}$ and $E_{22}$ excitons, we observed a small but unambiguous absorption peak whose intensity is maximum for perpendicular-polarized light. We attribute this feature to the lowest-energy cross-polarized interband absorption processes that change the angular momentum along the nanotube axis by $\pm 1$, generating $E_{12}$ and $E_{21}$ excitons. The energy difference between the $E_{12}$ and $E_{21}$ exciton peaks, expected from asymmetry between the conduction and valence bands, was smaller than the observed linewidth. Unlike previous observations of cross-polarized excitons in polarization-dependent photoluminescence and circular dichroism spectroscopy experiments, our direct observation using absorption spectroscopy allowed us to quantitatively analyze this resonance. Specifically, we determined the energy and oscillator strength of this resonance to be 1.54 and 0.05, respectively, compared with the values for the $E_{11}$ exciton peak. These values, in combination with comparison with theoretical calculations, in turn led to an assessment of the environmental effect on the strength of Coulomb interactions in this aligned single-chirality SWCNT film.

arXiv comment14 pages, 14 figures

References in corpus (8)

• Excitonic Effects and Optical Spectra of Single-Walled Carbon Nanotubes
• Scaling of excitons in carbon nanotubes
• Exciton binding energies in carbon nanotubes from two-photon photoluminescence
• Electron-electron interaction effects on optical excitations in semiconducting single-walled carbon nanotubes
• Excitons in carbon nanotubes: an ab initio symmetry-based approach
• The Ratio Problem in Single Carbon Nanotube Fluorescence Spectroscopy
• Cross-polarized optical absorption of single-walled nanotubes probed by polarized photoluminescence excitation spectroscopy
• Electron-Hole Asymmetry in Single-Walled Carbon Nanotubes Probed by Direct Observation of Transverse Quasi-Dark Excitons

Cited by in corpus (7)

• Science and applications of wafer-scale crystalline carbon nanotube films prepared through controlled vacuum filtration
• One-directional thermal transport in densely aligned single-wall carbon nanotube films
• Global alignment of solution-based single-wall carbon nanotube films via machine-vision controlled filtration
• Macroscopically Self-Aligned and Chiralized Carbon Nanotubes: From Filtration to Innovation
• Transition from Diffusive to Superdiffusive Transport in Carbon Nanotube Networks via Nematic Order Control
• Exciton lasing in carbon nanotubes below the population inversion threshold via phonon-mediated stimulated emission
• Origin of the Background Absorption in Carbon Nanotubes: Phonon-Assisted Excitonic Continuum