Coherent Phonons in Carbon Nanotubes and Graphene

TL;DR

This review discusses recent advances in understanding coherent phonons in carbon nanotubes and graphene, highlighting their excitation, detection, and potential for chirality determination, with theoretical insights into phonon dynamics and diameter changes.

Contribution

It provides a comprehensive review of experimental and theoretical studies on coherent phonons in carbon nanotubes and graphene, including new models for phonon excitation and diameter modulation.

Findings

RBM-CPs cause bandgap oscillations in SWCNTs.

Interband resonances enhance CP signals for chirality detection.

Diameter can initially increase or decrease upon excitation.

Abstract

We review recent studies of coherent phonons (CPs) corresponding to the radial breathing mode (RBM) and G-mode in single-wall carbon nanotubes (SWCNTs) and graphene. Because of the bandgap-diameter relationship, RBM-CPs cause bandgap oscillations in SWCNTs, modulating interband transitions at terahertz frequencies. Interband resonances enhance CP signals, allowing for chirality determination. Using pulse shaping, one can selectively excite speci!c-chirality SWCNTs within an ensemble. G-mode CPs exhibit temperature-dependent dephasing via interaction with RBM phonons. Our microscopic theory derives a driven oscillator equation with a density-dependent driving term, which correctly predicts CP trends within and between (2n+m) families. We also find that the diameter can initially increase or decrease. Finally, we theoretically study the radial breathing like mode in graphene nanoribbons. For excitation near the absorption edge, the driving term is much larger for zigzag nanoribbons. We also explain how the armchair nanoribbon width changes in response to laser excitation.