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.

中文翻译：

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长程相关在无序系统高次谐波产生中的作用

由于结构的多样性和复杂性，超快激光驱动的凝聚态物质产生高次谐波 (HHG) 的机制远未被理解。长期悬而未决的问题之一是随机无序对非晶体 HHG 的影响。在这项工作中，我们确定了相关性在无序半导体系统中的关键作用，并提出将它们作为对 HHG 过程进行分类的标准。HHG 谱可分为对应不同相关性的两个不同类别：短程相关性和长程相关性 (LRC)。因此，相关性在 HHG 排放和无序系统的统计特征之间建立了牢固的关系。尤其，来自具有 LRC 的无序系统的 HHG 光谱与来自周期格的光谱表现出显着的一致性，表明 LRC 链接无序和周期系统中的 HHG 过程。此外，由长程相关障碍引起的移动边缘使我们能够研究一个系统中局部和离域状态 HHG 的行为。