We theoretically investigate the piezo-optic effect of high-harmonic generation (HHG) in shear-strained semiconductors. By focusing on a typical semiconductor, GaAs, we show that there is optical activity, meaning different responses to right-handed
and left-handed elliptically polarized electric fields. We also show that this optical activity is more pronounced for higher harmonics whose perturbative order exceeds the band-gap energy. These findings point to a useful pathway for strain engineering of nonlinear optics to control the reciprocity of HHG.
We experimentally study the field-intensity dependence of high-harmonic generation in bulk gallium arsenide in reflection geometry. We find the oscillatory behavior at high fields where a perturbative scaling law no longer holds. By constructing a th
eoretical framework based on the Luttinger-Kohn model, we succeed in reproducing the observed oscillatory behavior. The qualitative agreement between the experiment and theory indicates that field-induced dynamic band modification is crucial in the nonperturbative regime. We consider the origin of the oscillatory behavior in terms of dynamical localization based on the Floquet subband picture.
We propose a novel picture of high-harmonic generation (HHG) in solids based on the concept of temporally changing band structures. To demonstrate the utility of this picture, we focus on the high-order sideband generation (HSG) caused by strong tera
hertz (THz) and weak near-infrared (NIR) light in the context of pump-probe spectroscopy. We find that the NIR frequency dependence of the HSG indicates the existence of new energy levels (sub-bands) around the band-gap energy, which have multiple frequencies of THz light. This sub-band picture explains why the HSG intensity becomes a non-monotonic function of the THz light amplitude. The present analysis not only reveals the origin of the plateau structure in HHG spectra, but also provides a connection to other high-field phenomena.
We theoretically investigate surface plasmon polaritons propagating in the thin-film Weyl semimetals. We show how the properties of surface plasmon polaritons are affected by hybridization between plasmons localized at the two metal-dielectric interf
aces. Generally, this hybridization results in new mixed plasmon modes, which are called short-range surface plasmons and long-range surface plasmons, respectively. We calculate dispersion curves of these mixed modes for three principle configurations of the axion vector describing axial anomaly in Weyl semimetals. We show that the partial lack of the dispersion and the non-reciprocity can be controlled by fine-tuning of the thickness of the Weyl semimetals, the dielectric constants of the outer insulators, and the direction of the axion vector.
We theoretically investigate detuning-dependent properties of high-order harmonic generation (HHG) in monolayer transition metal dichalcogenides (TMDCs). In contrast to HHG in conventional materials, TMDCs show both parallel and perpendicular emissio
ns with respect to the incident electric field. We find that such an anomalous emission can be artificially controlled by the frequency detuning of the incident electric fields, i.e., the parallel and perpendicular HHG can be strongly enhanced by multiphoton resonances. This peculiar phenomenon would provide a way for controlling HHG in TMDCs and stimulate the realization of novel optical devices.
We theoretically investigate the orientation dependence of high-harmonic generation (HHG) in monolayer transition metal dichalcogenides (TMDCs). We find that, unlike conventional solid-state and atomic layered materials such as graphene, both paralle
l and perpendicular emissions with respect to the incident electric field exist in TMDCs. Interestingly, the parallel (perpendicular) emissions principally contain only odd-(even-) order harmonics. Both harmonics show the same periodicity in the crystallographic orientations but opposite phases. These peculiar behaviors can be understood on the basis of the dipole moments in TMDCs, which reflect the symmetries of both atomic orbitals and lattice structures. Our findings are qualitatively consistent with recent experi- mental results and provide a possibility for high-harmonic spectroscopy of solid-state materials.
