Multiplateau structure caused by spectral interference in high-order harmonic generation from disordered Su-Schrieffer-Heeger chains

The multiple-plateau structure is a characteristic of high-order harmonic spectra in solids, resulting from strong interband couplings involving three or more bands. Here we show that high-order harmonic generation (HHG) in a two-band Su-Schrieffer-Heeger (SSH) system also exhibits a multiple-plateau structure under disorder effect. For weak external driving fields, the harmonic spectrum of disordered SSH chains exhibits an additional plateau and has a higher cutoff frequency compared with that of ordered SSH chains. The phase analysis of the harmonic spectra from various disordered SSH chains reveals that the second HHG plateau emerges from the interference between different regions. Through time-frequency analysis, we show that the harmonic phase corresponding to the caustic point is more localized than its neighboring orders.