Tunable Infrared Phonon Anomalies in Trilayer Graphene

TL;DR

This study reveals that trilayer graphene exhibits significant, tunable infrared phonon anomalies that depend on stacking order and electrostatic gating, highlighting strong electron-phonon interactions.

Contribution

It demonstrates the stacking-dependent tunability of infrared phonon responses in trilayer graphene and models these effects with a charged-phonon framework.

Findings

Enhanced phonon absorption in ABC-stacked graphene with gating

Softening of phonon modes as Fermi level shifts

Stacking order influences electron-phonon coupling strength

Abstract

Trilayer graphene in both ABA (Bernal) and ABC (rhombohedral) stacking sequences is shown to exhibit intense infrared absorption from in-plane optical phonons. The feature, lying at ~1580 cm-1, changes strongly with electrostatic gating. For ABC-stacked graphene trilayers, we observed a large enhancement in phonon absorption amplitude, as well as softening of the phonon mode, as the Fermi level is tuned away from charge neutrality. A similar, but substantially weaker effect is seen in samples with the more common ABA stacking order. The strong infrared response of the optical phonons and the pronounced variation with electrostatic gating and stacking-order reflect the interactions of the phonons and electronic excitations in the two systems. The key experimental findings can be reproduced within a simplified charged-phonon model that considers the influence of charging through Pauli blocking of the electronic transitions.