Anomalous Optical Phonon Splittings in Sliding Bilayer Graphene

TL;DR

This paper investigates how sliding in bilayer graphene affects optical phonon modes and their spectroscopic signatures, revealing sensitive dependence on symmetry and electronic interactions, with potential for detecting layer misalignment.

Contribution

It introduces a first-principles and model-based analysis of phonon mode variations due to sliding, highlighting the role of symmetry and electronic coupling in anomalous behaviors.

Findings

Optical phonon modes exhibit sensitive changes depending on sliding direction and symmetry.

Interlayer electronic coupling critically influences phonon mode renormalization.

Sliding-induced symmetry changes alter Raman scattering intensities, enabling misalignment detection.

Abstract

We study the variations of electron-phonon coupling and their spectroscopic consequences in response to sliding of two layers in bilayer graphene using first-principles calculations and a model Hamiltonian. Our study shows that the long wave-length optical phonon modes change in a sensitive and unusual way depending on the symmetry as well as the parity of sliding atomic structures and that, accordingly, Raman- and infrared-active optical phonon modes behave differently upon the direction and size of the sliding. The renormalization of phonon modes by the interlayer electronic coupling is shown to be crucial to explain their anomalous behavior upon the sliding. Also, we show that the crystal symmetry change due to the sliding affects the polarized Stokes Raman-scattering intensity, which can be utilized to detect tiny misalignment of graphene layers using spectroscopic tools.