Extreme renormalisations of dimer eigenmodes by strong light–matter coupling

Abstract

Abstract We explore by theoretical means an extreme renormalisation of the eigenmodes of a dimer of dipolar meta-atoms due to strong light–matter interactions. Firstly, by tuning the height of an enclosing photonic cavity, we can lower the energy level of the symmetric ‘bright’ mode underneath that of the anti-symmetric ‘dark’ mode. This is possible due to the polaritonic nature of the symmetric mode, that shares simultaneously its excitation with the cavity and the dimer. For a heterogeneous dimer, we show that the polariton modes can be smoothly tuned from symmetric to anti-symmetric, resulting in a variable mode localisation from extended throughout the cavity to concentrated around the vicinity of the dimer. In addition, we reveal a critical point where one of the meta-atoms becomes ‘shrouded’, with no response to a driving electric field, and thus the field re-radiated by the dimer is only that of the other meta-atom. We provide an exact analytical description of the system from first principles, as well as full-wave electromagnetic simulations that show a strong quantitative agreement with the analytical model. Our description is relevant for any physical dimer where dipolar interactions are the dominant mechanism.