Fig. 1. (a) Crystal structure and unit cell of ZGNR composed of N zigzag carbon lines. (b), (c) Band structure of ZGNR whose width is 4 and 15 used in our simulations.

Fig. 2. (a), (b) Intensity variation of HHG with the pump laser wavelength ranging from 800 nm to 3600 nm. The ZGNR width N is four and the pump laser intensity is 1TW/cm2. (c) Wavelength linear dependence of the cutoff energy in ZGNR’s HHG.

Fig. 3. (a)–(f) High harmonic spectra of ZGNR with different widths (N=2, 3, 4, 7, 10, 15), where the blue solid curves denote the normal harmonic spectra, and the red dashed curves represent the harmonic spectra contributed only by the edge states.

Fig. 4. Typical yield of 3rd, 5th, 15th, and 25th harmonics, depending on the ZGNR width. The solid lines marked with circles are the normal harmonics, while the dashed curves with diamond marks denote harmonics yield generated only by edge states.