Role of long-range correlations in high harmonic generation in disordered systems

The mechanism of high harmonic generation (HHG) from condensed matter driven by ultrafast lasers is far from being understood due to the structural diversity and complexity. One of the long-standing open questions is the effect of random disorder in noncrystal HHG. In this work, we identify the critical role of correlations in disordered semiconductor systems and propose them as the criterion to classify the HHG processes. The HHG spectra can be classified into two different categories corresponding to different correlations: short-range correlation and long-range correlation (LRC). Thus correlations build up a solid relationship between the HHG emission and statistical characteristics of a disordered system. In particular, the HHG spectrum from the disordered system with LRC exhibits remarkable consistency with the spectrum from the periodic lattice, revealing that the LRC links HHG processes in disordered and periodic systems. Besides, the mobility edge induced by the long-range correlated disorder enables us to study the behavior of localized- and delocalized-state HHG in one system.