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

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 F ∼ 10nN/nm 2 leading to a giant shear displacement Q0 ∼ 50pm 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 Q0 in different electronic doping, temperature, and scattering rates. We reveal that the finite Q0 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.