  Chirality is an intriguing property of certain molecules, materials or
artificial nanostructures, which allows them to interact with the spin angular
momentum of the impinging light field. Due to their chiral geometry, they can
distinguish between left- and right-hand circular polarization states or
convert them into each other. Here, we introduce a novel approach towards
optical chirality, which is observed in individual two-dimensional and
geometrically mirror-symmetric nanostructures. In this scheme, the chiral
optical response is induced by the chosen heterogeneous material composition of
a particle assembly and the corresponding resonance behavior of the
constituents it is built from, which breaks the symmetry of the system. As a
proof of principle, we investigate such a structure composed of individual
silicon and gold nanoparticles both experimentally as well as numerically. Our
proposed concept constitutes a novel approach for designing two-dimensional
chiral media tailored at the nanoscale.
