  We investigate a geometrically symmetric gold-silicon sphere heterodimer and
reveal its extrinsic chiroptical response caused by the interaction with a
substrate. The chiroptical response is obtained for oblique incidence owing to
the coalescence of extrinsic chirality, heterogeneity and substrate induced
break of symmetry. To quantify the chiral response we utilize k-space
polarimetry. We elucidate the physics of the involved phenomena by considering
scattering properties of the heterodimer in free space and find that incident
linearly polarized light is scattered in a spin-split fashion. We corroborate
our finding with a coupled dipole model and find that the spin-split behavior
originates from the heterogeneity of the structure. This spin-split scattering,
combined with the substrate-induced break of symmetry, leads to an extrinsic
chiroptical response. Our work sheds new light on the potential and optical
properties of heterogeneous nanostructures and paves the way for designing
spectrally tunable polarization controlled heterogeneous optical elements.
