Optical Phonon Lineshapes and Transport in Metallic Carbon Nanotubes under High Bias Voltage

TL;DR

This paper models the current-voltage behavior of metallic carbon nanotubes at high bias, revealing phonon redistribution effects and predicting phonon frequency shifts consistent with experiments.

Contribution

It provides an analytical framework for understanding phonon and electron distributions and their impact on optical phonon lineshapes under high bias in nanotubes.

Findings

Short nanotubes exhibit a current bottleneck at high bias.

Positive frequency shift of optical phonons observed at high voltages.

No broadening of optical phonon modes at very high voltages.

Abstract

We calculate the current-voltage characteristic of metallic nanotubes at high bias voltage showing that a bottleneck exists for short nanotubes in contrast to large ones. We attribute this to a redistribution of lower-lying acoustic phonons caused by phonon-phonon scattering with hot optical phonons. The current-voltage characteristic and the electron and phonon distribution functions are derived analytically, and serve to obtain in a self-contained way the frequency shift and line broadening of the zone center optical phonons due to the electron-phonon coupling at high bias. We obtain a positive frequency shift from the zero bias shift and no broadening of the optical phonon mode at very high voltages, in agreement with recent experiments.