Coherent radial breathing like phonons in graphene nanoribbons

TL;DR

This paper presents a microscopic theory for generating and detecting coherent phonons in graphene nanoribbons, revealing how excitation energy and nanoribbon type influence phonon amplitudes and responses.

Contribution

It introduces a detailed microscopic model combining electronic and phononic calculations to analyze coherent phonon dynamics in armchair and zigzag graphene nanoribbons.

Findings

Coherent phonon amplitudes are larger near the optical absorption edge.

Zigzag nanoribbons exhibit stronger driving of radial breathing modes due to edge states.

Laser excitation affects nanoribbon width via phonon interactions.

Abstract

We have developed a microscopic theory for the generation and detection of coherent phonons in armchair and zigzag carbon nanoribbons using an extended tight-binding model for the electronic states and a valence force field model for the phonons. The coherent phonon amplitudes satisfy a driven oscillator equation with the driving term depending on photoexcited carrier density. We examine the coherent phonon radial breathing like mode amplitudes as a function of excitation energies and nanoribbon types. For photoexcitation near the optical absorption edge the coherent phonon driving term for the radial breathing like mode is much larger for zigzag nanoribbons where transitions between localized edge states provide the dominant contribution to the coherent phonon driving term. Using an effective mass theory, we explain how the armchair nanoribbon width changes in response to laser excitation.