Unidirectional scattering induced by magnetic dipoles in core–shell nanostructures

Abstract

Unidirectional scattering is typically achieved through the interference of induced electric and magnetic dipole modes in nanophotonics. However, there are limited studies on achieving unidirectional scattering solely through magnetic dipole (MD) moments. Here, we propose and demonstrate that the extraordinary unidirectional scattering can be obtained in a pair of closely spaced MDs in a Si–Au core–shell dimer. The conditions for such unidirectional scattering are derived using the dipole approximation. Calculated with the coupled dipole method, a pronounced unidirectionality (up to 60 dB) in the forward scattering can be achieved with the dimer system. This can be attributed to the destructive interference of scattered far field from the induced MDs. Interestingly, the scattering direction could be controlled by varying the position of the element in the dimer and the main lobe angle of the far field can be efficiently induced by the antenna array. Furthermore, a remarkable forward-to-backward directionality can also be achieved when a magnetic dipole emitter is close to the Si–Au core–shell particle. These findings indicate the potential of this simple yet versatile platform for manipulating scattering.