Chirality dependence of electron-phonon matrix elements in semiconducting single-walled carbon nanotubes

Takumi Inaba,Yoshikazu Homma

doi:10.1063/1.5093066

Abstract

Evaluations of quantum coupling between electrons and phonons in well-defined nanostructure will be necessary when applications based on the vibrations of various materials move into the quantum regime. Raman scattering, in which changes in polarization within a material are probed by light, is an excellent means of analyzing electron-phonon coupling. In this study, the Raman intensities of individually suspended single-walled carbon nanotubes were determined in order to examine variations in electron-phonon interactions in response to changes in the arrangement of carbon atoms (i.e., chirality). Unambiguous assignment of nanotube chirality was achieved by photoluminescence spectroscopy and similar variations in the radial breathing mode and intermediate frequency mode peak intensities with changes in chirality were found. These phenomena were explained based on prior theoretical studies. The D-mode and G-mode peaks were also observed to respond in the same manner, based on which we assigned the longitudinal optical phonon branch to the D-mode. The results of this work demonstrate that the Raman intensity analysis can provide useful information regarding electron-phonon coupling in nanomaterials.

Highlights

Resonant Raman scattering from single-walled carbon nanotubes (SWCNTs) provides a means for assessing quantum hybridization
In the case of semiconducting SWCNTs, the momentum of phonons is restricted because the momentum separation between the minima of two real-state electron bands necessarily corresponds to a near K-momentum vector in the graphene Brillouin zone
The results show that the effects of chirality on the RBM and IFM are similar because both belong to the same phonon branch

Summary

INTRODUCTION

Resonant Raman scattering from single-walled carbon nanotubes (SWCNTs) provides a means for assessing quantum hybridization. In resonant Raman scattering, using incident light resonance conditions as an example, real-state electrons are generated by photon absorption. The fact that K-momentum phonons in SWCNTs are optically probed via the double resonant Raman scattering is intriguing. Scitation.org/journal/adv states of optical phonons near K-points in the graphene Brillouin zone. Another reason may stem from the ambiguous definition of longitudinal (LO) and transverse optical (TO) oscillations in SWCNTs.. In the range of 400-500 cm-1, is ascribed to the double resonant process, meaning that the IFM has a value the K-momentum.13,14 The origin of this IFM is the out-of-plane acoustic phonon branch of graphene that transforms to an “acoustic-like” optical branch in the tubular structure of SWCNTs In the range of 400-500 cm-1, is ascribed to the double resonant process, meaning that the IFM has a value the K-momentum. The origin of this IFM is the out-of-plane acoustic phonon branch of graphene that transforms to an “acoustic-like” optical branch in the tubular structure of SWCNTs

CHIRALITY-DEPENDENT RAMAN SPECTRA

INTENSITY ANALYSIS

CONCLUSION