Semiclassical analysis of ellipticity dependence of harmonic yield in graphene

We theoretically investigate the ellipticity dependence of high-order harmonic generation in graphene driven by the midinfrared laser field. The ellipticity dependence of the harmonic yield in the experiment [N. Yoshikawa, T. Tamaya, and K. Tanaka, Science 356, 736 (2017)] is reproduced perfectly by solving the semiconductor Bloch equations in the Houston basis under the tight-binding approximation. Based on the semiclassical recollision model, it is found that the recollision distance of the electron-hole pair excited from the zone 0.5 omega(0) <=Delta E <= 2.5 omega(0) instead of the Dirac points can reach a minimum value at finite ellipticity, which enhances the harmonic yield. In addition, the ellipticity dependence of harmonics can be controlled by varying the chemical potential of graphene. When the chemical potential is decreased to -1.52 eV, the ellipticity dependence of harmonics can transit into the normal behavior. This work uncovers the microscopic mechanism of the ellipticity dependence of the harmonics in graphene and constructs a clear physical picture to understand the unique ellipticity-dependent behaviors in graphene.