Giant Shear Displacement by Light-Induced Raman Force in Bilayer Graphene

TL;DR

This paper develops a theoretical framework to demonstrate that intense infrared lasers can induce giant shear displacements in bilayer graphene via Raman forces, enabling control over electronic properties and phase transitions.

Contribution

The study introduces a diagrammatic theory for displacive Raman forces and predicts significant shear displacements in bilayer graphene, tunable by laser parameters and electronic conditions.

Findings

Giant shear displacement of ~50 pm induced by laser.

Raman force density of ~10 nN/nm^2 in bilayer graphene.

Laser parameters can tune electronic structure and phase transitions.

Abstract

Coherent excitation of shear phonons in van der Waals layered materials is a non-destructive mechanism to fine-tune the electronic state of the system. We develop a diagrammatic theory for the displacive Raman force and apply it to the shear phonon's dynamics. We obtain a rectified Raman force density in bilayer graphene of the order of ${\cal F}\sim 10{\rm nN/nm^2}$ leading to a giant shear displacement $Q_0 \sim 50$pm for an intense infrared laser. We discuss both circular and linear displacive Raman forces. We show that the laser frequency and polarization can effectively tune $Q_0$ in different electronic doping, temperature, and scattering rates. We reveal that the finite $Q_0$ induces a Dirac crossing pair in the low-energy dispersion that photoemission spectroscopy can probe. Our finding provides a systematic pathway to simulate and analyze the coherent manipulation of staking order in the heterostructures of layered materials by laser irradiation.