Effect of asymmetry on nonlinear optical response in graphene
We show that a slight asymmetry in the wave function of graphene can result in a significant enhancement of the nonlinear effect on the optical response. The third-order nonlinear current due to asymmetry modification of the wave function increases with kFa, where kF is the Fermi eigenvector and a is the lattice constant. The effect of asymmetry can significantly enhance the third-order current at low temperature and at large Fermi energies. For kFa around 1, the nonlinear current increases by around 40% at low temperatures.