Plasmonics is a rapidly developing field at the boundary of physical optics and condensed matter physics. It studies phenomena induced by and associated with surface plasmons—elementary polar excitations bound to surfaces and interfaces of good nanostructured metals. This Roadmap is written collectively by prominent researchers in the field of plasmonics. It encompasses selected aspects of nanoplasmonics. Among them are fundamental aspects, such as quantum plasmonics based on the quantum-mechanical properties of both the underlying materials and the plasmons themselves (such as their quantum generator, spaser), plasmonics in novel materials, ultrafast (attosecond) nanoplasmonics, etc. Selected applications of nanoplasmonics are also reflected in this Roadmap, in particular, plasmonic waveguiding, practical applications of plasmonics enabled by novel materials, thermo-plasmonics, plasmonic-induced photochemistry and photo-catalysis. This Roadmap is a concise but authoritative overview of modern plasmonics. It will be of interest to a wide audience of both fundamental physicists and chemists, as well as applied scientists and engineers.

We demonstrate an innovative concept for nanoscale electro-optic switching. It exploits the frequency shift of a narrow-band Fano resonance mode in a plasmonic planar metamaterial induced by a change in the dielectric properties of an adjacent chalcogenide glass layer. An electrically stimulated transition between amorphous and crystalline forms of the glass brings about a 150 nm shift in the near-infrared resonance providing transmission modulation with a contrast ratio of 4:1 in a device of subwavelength thickness.

Chalcogenides—alloys based on group-16 ‘chalcogen’ elements (sulfur, selenium, and tellurium) covalently bound to ‘network formers’ such as arsenic, germanium, antimony, and gallium—have a variety of technologically useful properties, including infrared transparency, high optical nonlinearity, photorefractivity and readily induced, reversible, non-volatile structural phase switching. Such phase-change materials are of enormous interest in the fields of plasmonics and nanophotonics. However, in such applications, the fact that some chalcogenides accrue plasmonic properties in the transition from an amorphous to a crystalline state, i.e., the real part of their relative permittivity becomes negative, has gone somewhat unnoticed. Indeed, one of the most commercially important chalcogenide compounds, germanium antimony telluride (Ge₂:Sb₂:Te₅ or GST), which is widely used in rewritable optical and electronic data storage technologies, presents this behavior at wavelengths in the near-ultraviolet to visible spectral range. In this work, we show that the phase transition-induced emergence of plasmonic properties in the crystalline state can markedly change the optical properties of sub-wavelength-thickness, nanostructured GST films, allowing for the realization of non-volatile, reconfigurable (e.g., color-tunable) chalcogenide metasurfaces operating at visible frequencies and creating opportunities for developments in non-volatile optical memory, solid state displays and all-optical switching devices.