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Abstract

Recently, we introduced an ab-initio time-dependent density-functional theory (TDDFT) framework that allows us to investigate the coupled interplay between the interband and intraband mechanisms of high-harmonic generation (HHG) from solids [1] without making a-priori model assumptions or strong approximations. Here, using HHG experiments on bulk silicon samples combined with TDDFT simulations, we study the complex physics underlying anisotropic harmonic emission, as reported by You et al. [2] for the strongly anisotropic ellipticity dependence of the 19th harmonic (HH19) generated in bulk MgO. In [2], the observed anisotropy was explained with real-space trajectories in a 2D one-band model including scattering from neighboring atomic sites. Our TDDFT simulations [3] and HHG experiments reveal that the various higher-harmonic orders generated in solids exhibit qualitatively different sensitivity to driver-pulse ellipticity ε (not displayed here), resulting from a different response of intraband and interband dynamics [3], in contradiction with the model proposed in [2]. In fact, band-structure and joint-density-of-states (JDOS) effects become important [1].