Tunable Quantum-Enhanced Second-Order Optical Nonlinearity From Bilayer Graphene

Bilayer graphene exhibits a tunable band gap when the inversion symmetry is broken. It therefore stimulates much interest on its physical characterization and practical application for mid-infrared (MIR) optoelectronics. Here we focus on its second order nonlinear optical response to the MIR laser excitation under device condition, following a quantum description of nonlinear optical conductivity. Our theoretical study shows that, for a certain laser-frequency range determined by the band-gap, giant second harmonic generation can be excited due to the intrinsic electronic spectrum of bilayer graphene. Electrically tunable $\chi ^{(2)}$ on the order of $10^5pm/V$ can be achieved, 3 orders of magnitude larger than the widely-used nonlinear crystal AgGaSe2.