High-order harmonic generation from periodic asymmetric potentials

High-order harmonic generation (HHG) from periodic asymmetric potentials is investigated by solving the real-space time-dependent Schrodinger equations and semi-conductor Bloch equations. Our results show that the periodic asymmetric potential will cause asymmetric excitation and HHG dynamics in the time domain, leading to the signal of even order harmonics. From the k-space perspective, a k-dependent transition dipole moment phase reflects the real-space asymmetry and causes the symmetry breaking of excitation and HHG dynamics. We also illustrate that the dephasing effect competes with the asymmetry of interband HHG dynamics. Large amplitude of the driving field is beneficial for observing the symmetry breaking of interband HHG. However, it is found symmetry breaking of intraband HHG dynamics is less influenced by dephasing. Moreover, a carrier-envelope phase controlled driving laser field can be utilized as an isolated attosecond pulse gating mechanism for HHG from the periodic asymmetric potentials.