  Nonlinear chiral photonics explores nonlinear response of chiral structures,
and it offers a pathway to novel optical functionalities not accessible through
linear or achiral systems. Here we present the first application of
nanostructured van der Waals materials to nonlinear chiral photonics. We
demonstrate the three orders of magnitude enhancement of the third-harmonic
generation from hBN metasurfaces driven by quasi-bound states in the continuum,
accompanied by a strong nonlinear circular dichroism in the resonant
metasurface varying from the values -0.5 to +0.5. This novel platform for
chiral metaphotonics can be employed for achieving large circular dichroism
combined with high-efficiency harmonic generation in a broad frequency range.
