Signature of a Fano-resonance in a plasmonic meta-molecule's local density of optical states

We present measurements on plasmonic meta-molecules under local excitation using cathodoluminescence which show a spatial redistribution of the local density of optical states (LDOS) at the same frequency where a sharp spectral Fano-feature in the extinction cross section has been observed. Our analytical model shows that both near- and far-field effects arise due to interference of the same two eigenmodes of the system. We present quantitative insights both in a bare state, and in a dressed state picture that describe plasmonic Fano interference either as near-field amplitude transfer between three coupled bare states, or as interference of two uncoupled eigenmodes in the far field. We identify the same eigenmode causing a dip in extinction to strongly enhance the radiative LDOS, making it a promising candidate for spontaneous emission control.