Direct Observation of Mode Selective Electron−Phonon Coupling in Suspended Carbon Nanotubes

Raman spectra of individual pristine suspended single-walled carbon nanotubes are observed under high electrical bias. The LO and TO modes of the G band behave differently with respect to voltage bias, indicating preferential electron−phonon coupling and nonequilibrium phonon populations, which cause negative differential conductance in suspended devices. By correlating the electron resistivity to the optically measured phonon population, the data are fit using a Landauer model to determine the key scattering parameters. Electron-phonon coupling in carbon nanotubes has been studied by many research groups.1-7 In metallic carbon nanotubes (m-CNTs), conduction electrons have been pre-dicted to couple strongly to the ¡-point longitudinal optical (LO) phonons and to the 2kF-point transverse optical (TO) phonons.1-6 The G band Raman spectra of m-CNTs and semiconducting CNTs (s-CNT) are qualitatively different because of this strong electron-phonon coupling.8 In metallic nanotubes, the lower-frequency component of the G band (G-) exhibits a broad Breit-Wigner-Fano (BWF) line shap