  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.
