This sharp resonance is stronger than its well known counterpart, and tunable by varying shell thickness or having metal heterostructures. It exemplifies an important growing field – "Babinet's (principle) plasmonics" – in which the structure is mainly metal.

A metal-in-metal system is the Babinet's counterpart of insulator systems containing metal shells or rings, which have been studied for a decade for their geometric tunability and hybrid plasmon modes.

Exciting science and numerous applications for this new resonant class of materials are envisaged. For example, large-area flexible 2D examples mass produced in thin metal layers should be practical, with the challenge to see how thin the insulator rings can go.

The researchers presented their work in the journal Nanotechnology.