Molecular aggregates
are a fascinating and important class of materials,
particularly in the context of optical (pigmented) materials. In nature,
molecular aggregates are employed in photosynthetic light harvesting
structures, while synthetic aggregates are employed in new generation
molecular sensors and magnets. The roles of disorder and symmetry
are vital in determining the photophysical properties of molecular
aggregates, but have been hard to investigate experimentally, owing
to a lack of sufficient structural control at the molecular level
and the challenge of probing their optical response with molecular
spatial resolution. We present a new approach using microwave analogues
of molecular aggregates to study the properties of both individual
meta-molecules and 1D molecular chains. We successfully replicate
J- and H-aggregate behavior and demonstrate the power of our approach
through the controlled introduction of structural symmetry breaking.
Our results open a new area of study, combining concepts from molecular
science and metamaterials.
Passive resonant metamaterials are limited by the narrow-band nature of the resonances they support. Here we show that by incorporating an active component into the structure of the commonly used split-ring resonator it is possible to tune the resonance frequency of this type of metamaterial atom. We make use of this tunability to examine the interaction between two resonators, one passive and one active, as the resonance frequency of the active resonator is swept through that of the passive resonator. The resultant modes of this coupled system exhibit an anticrossing and, by changing the separation between, and relative orientation of, the split-ring resonators, we investigate how the magnetic and electric coupling terms change. We find that the relative orientation of the resonators significantly effects the strength of the coupling. Through both structural and active tuning we are able to alter the relative sizes and signs of the coupling terms. We hope that the nature of these changes will be of use to those designing large actively tunable metamaterial systems.
The formation of polariton modes due to the strong coupling of light and matter has led to exciting developments in physics, chemistry, and materials science. The potential to modify the properties of molecular materials by strongly coupling molecules to a confined light field is so far-reaching and so attractive that a new field known as "polaritonic chemistry" is now emerging. However, the molecular scale of the materials involved makes probing strong coupling at the individual resonator level extremely challenging. Here, we offer a complementary approach based upon metamaterials, an approach that enables us to use cm-scale structures, thereby opening a new way to explore strong coupling phenomena. As proof-ofprinciple, we show that metamolecules placed inside a radio frequency cavity may exhibit strong coupling and show that near-field radio frequency techniques allow us, for the first time, to probe the response of individual metamolecules under strong coupling conditions.
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