Non-perturbative nonlinear optical responses in Weyl semimetals

We report a systematic and detailed investigation on strong-field driven non-perturbative high-harmonic generation from Weyl semimetals in various realistic environments, i.e., going beyond the idealistic situation where the Weyl nodes are at Fermi energy and are energy degenerate. Two classes of topological semimetals are considered: time-reversal broken Weyl semimetal and inversion-symmetry broken Weyl semimetal. It has been found that type-II Weyl semimetal leads to significant enhancement in the yield of the higher-order harmonics. In addition, energy splitting between the Weyl nodes also results in a modest boost in the harmonic yield. The underlying mechanism responsible for the enhancement can be traced to a drastic increase in the conduction band electronic population and noticeable changes in the momentum matrix amplitude. A combined effect of the tilt in the Weyl cones and energy separation between the nodes allows the generation of forbidden even-order harmonics in inversion-symmetric Weyl semimetal. Our findings offer exciting avenues for Weyl semimetals in ultrafast photonics and optoelectronic devices.