Laser-driven parametric instability and generation of entangled   photon-plasmon states in graphene and topological insulators
  We show that a strong infrared laser beam obliquely incident on graphene can experience a parametric instability with respect to decay into lower-frequency (idler) photons and THz surface plasmons. The instability is due to a strong in-plane second-order nonlinear response of graphene which originates from its spatial dispersion. The parametric decay leads to efficient generation of THz plasmons and gives rise to quantum entanglement of idler photons and surface plasmon states. A similar process can be supported by surface states of topological insulators such as Bi$_2$Se$_3$. 
Mikhail Tokman, Yongrui Wang, Ivan Oladyshkin, A. Ryan Kutayiah,   Alexey Belyanin
quant-ph cond-mat.mes-hall physics.optics