High Harmonic generation in graphene quantum dot

We investigated theoretically the high harmonics generated from a graphene quantum dot, which has the shape of a disk. The energy spectrum of such a quantum dot is obtained from the effective Dirac Hamiltonian. Due to the finite size of the system, the energy spectrum has a finite bandgap. We consider the interaction of graphene quantum dot with ultrashort linearly polarized optical pulse and the corresponding dipole radiation from the system, which is characterized by the generation of high harmonics. With the pulse's amplitude of 0.3 V/A and the pulse duration of 15 femtoseconds, we observe high harmonics of up to the twenty-third order for a 15 nm diameter quantum dot. The contribution to the high harmonic generation from the interband and intraband energy levels is comparable. Finally, a cut-off frequency versus an applied field amplitude shows a linear dependence. We also studied how the size of the graphene quantum dot affects the high harmonic generation spectrum and the corresponding cut-off frequency. These findings can be used to further the knowledge and understanding of high harmonics in finite 2D graphene-like systems.