Pump-induced terahertz anisotropy in bilayer graphene

We investigate the intraband nonlinear dynamics in doped bilayer graphene presence of strong, linearly polarized, in-plane terahertz fields. perform degenerate pump-probe experiments with 3.4-THz fields on at low temperature ($12\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and find that when pump is copolarized probe beam, differential signal almost double found cross-polarized case. show origin this pump-induced anisotropy difference average electron effective mass direction carriers are displaced $k$ space by either parallel or perpendicular to polarization. model system using both a simple semiclassical Boltzmann equation simulation phenomenological scattering good qualitative agreement experimental results.