Fano profiles in Au-Ag dimers

The near field coupling between a gold and a silver spherical nanoparticle is investigated theoretically. Fano profiles are observed in the absorption cross section of the gold nanoparticle due to the coupling between the spectrally localized surface plasmon resonance of the silver nanoparticle and the continuum of interband transitions of the gold one. The effect of dimer internal characteristics (particles sizes and distance), surrounding medium (through the refractive index) and external excitation (polarization and propagation irections) are addressed. In particular, it is shown that the near field coupling can be tuned from the weak to the strong regime by rotating the polarization direction and that the Fano profiles are sensitive to the shadowing effect even for small particle sizes.