Fig. 1. The structure and the energy dispersion of a monolayer h-BN crystal

Fig. 2. The high harmonics as a function of the crystal orientation

Fig. 3. Intensity-dependence of the H17 and the high harmonics spectrum

Fig. 4. The intensities of the H17 generated by different momentum and the bandgaps along paths in reciprocal space marked by the red lines

Fig. 5. The bandgap along Γ-K'-K-Γ paths and the parallel components of the high harmonics after the band change

Fig. 6. Instantaneous electric field of the driving laser and time-frequency analysis of the harmonic current

Fig. 7. Phase difference between the harmonics of K and K' momentum channel