  We show how the elusive toroidal dipole moment appears as a radiative
excitation eigenmode in a metamolecule resonator that is formed by pairs of
plasmonic nanorods. We analyze one such nanorod configuration - a toroidal
metamolecule. We find that the radiative interactions in the toroidal
metamolecule can be qualitatively represented by a theoretical model based on
an electric point dipole arrangement. Both a finite-size rod model and the
point dipole approximation demonstrate how the toroidal dipole moment is
subradiant and difficult to excite by incident light. By means of breaking the
geometric symmetry of the metamolecule, the toroidal mode can be excited by
linearly polarized light and appears as a Fano resonance dip in the forward
scattered light. We provide simple optimization protocols for maximizing the
toroidal dipole mode excitation. This opens up possibilities for simplified
control and driving of metamaterial arrays consisting of toroidal dipole
unit-cell resonators.
