Phonon Linewidths and Electron Phonon Coupling in Nanotubes

TL;DR

This paper demonstrates that electron-phonon coupling is the primary cause of Raman peak broadening in nanotubes, enabling direct measurement and comparison with theoretical predictions, and clarifies spectral differences between metallic and semiconducting nanotubes.

Contribution

It provides direct measurement of EPCs from Raman linewidths and clarifies the origin of G and G- peaks in nanotubes, contrasting with previous Fano resonance interpretations.

Findings

EPC is the main source of Raman peak broadening in nanotubes.

Experimental EPCs match density functional theory calculations.

EPC explains spectral differences between metallic and semiconducting nanotubes.

Abstract

We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G and G- peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G- linewidths. The experimental EPCs compare extremely well with those from density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G- peak in metallic nanotubes to a Fano resonance between phonons and plasmons. We assign the G+ and G- peaks to TO (tangential) and LO (axial) modes.