Abstract
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.
*Major funding was provided by Grant No. DE-SC0007043 from the Materials Sciences and Engineering Division of the Office of the Basic Energy Sciences, Office of Science, U.S. Department of Energy. Numerical simulations were performed using support by Grant No. DE-FG02-01ER15213 from the Chemical Sciences, Biosciences, and Geosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy. The work of VA was supported by NSF EFRI NewLAW Grant No EFMA-1741691 with the sub-award No. T883032. Support for SAOM came from MURI Grant No. FA9550-15-1-0037 from the U.S. Air Force Office of Scientific Research and Office of Naval Research (DOD)Grant No. N000-14-17-1-2588 with the sub-award No. 24086151.
