Tunable nonlinear excitonic optical response in biased bilayer graphene

Biased bilayer graphene (BBG) is an important system for studies of excitonic effects in graphene-based systems, with its easily tunable band gap. This band gap is governed by an external gate voltage, allowing one to tune the optical response of the system. In this paper, we study the excitonic linear and nonlinear optical responses of Bernal-stacked BBG as a function of the gate voltage, both for in-plane (IP) and out-of-plane (OOP) directions. Based on a semianalytical model of the electronic structure of BBG describing the influence of gate voltage on excitonic binding energies, we focus our discussion on both the IP and OOP excitonic responses. Both linear and second harmonic generation nonlinear responses are shown to be very sensitive to the gate voltage, as both the interband momentum matrix elements and the band gap of the system will vary greatly with bias potential.