Electrons and photons can coexist as a single entity called a surface plasmon—an elementary excitation found at the interface between a conductor and an insulator. Because of their hybrid electric and photonic nature, plasmons allow photons to be precisely controlled on the nanoscale. Plasmons are evident in the vivid hues of rose windows, which derive their color from small metallic nanoparticles embedded in the glass. They also provide the basis for color-changing biosensors (such as home pregnancy tests), photothermal cancer treatments, improved photovoltaic cell efficiencies, and nanoscale lasers. While surface plasmons were first identified nearly 55 years ago, many of their exciting applications are yet to come. This issue of MRS Bulletin reviews the progress and promise of plasmonics—from the characterization tools that have allowed nanometer-scale probing of plasmons to the new materials that may enable low-loss, active, and quantum plasmonics. Within reach are applications ranging from integrated plasmonic circuits for nanophotonic computation to plasmonic optical tweezers for manipulation of nano-sized particles and proteins.
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