Chiral Dichroism in Resonant Metasurfaces with Monoclinic Lattices

We demonstrate that chiral response can be achieved in resonant metasurfaces with a monoclinic lattice symmetry (the so-called Bravais oblique lattices) where the mirror symmetry is broken by the lattice asymmetry and also by a substrate, whereas each individual meta-atom remains fully achiral. We describe the underlying physics by introducing a mode chirality parameter as a quantitative measure of the lattice chiral eigenmodes. We confirm experimentally selective linear and nonlinear chiral interaction of resonant silicon metasurfaces with circularly polarized light.