Because plasmonic modes have no cut-off, we are able to demonstrate downscaling

The emerging field of nano-photonics 1 addresses the challenge of manipulating light on scales much smaller than the wavelength although very few practical approaches exist at present. Surface plasmon polaritons (SPP)2

Nanoplasmonics has recently revolutionized our ability to control light on the nanoscale. Using metallic nanostructures with tailored shapes, it is possible to efficiently focus light into nanoscale field ‘hot spots'. High field enhancement factors have been achieved in such optical nanoantennas, enabling transformative science in the areas of single molecule interactions, highly enhanced nonlinearities and nanoscale waveguiding. Unfortunately, these large enhancements come at the price of high optical losses due to absorption in the metal, severely limiting real-world applications. Via the realization of a novel nanophotonic platform based on dielectric nanostructures to form efficient nanoantennas with ultra-low light-into-heat conversion, here we demonstrate an approach that overcomes these limitations. We show that dimer-like silicon-based single nanoantennas produce both high surface enhanced fluorescence and surface enhanced Raman scattering, while at the same time generating a negligible temperature increase in their hot spots and surrounding environments.

*These authors contributed equally to this work.Plasmon lasers create and sustain coherent surface plasmon polaritons, collective electronic oscillations of metal-dielectric interfaces (1-5). These intense, coherent and confined optical fields have the unique ability to drastically enhance light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications (5-7). However, these important applications require sub-diffraction limited lasers operating at room temperature, which remains a major hurdle (1, 2). There are two critical challenges: high absorptive loss of metals and low cavity feedback. Recent efforts in semiconductor plasmon lasers have resulted in two approaches: devices capped in metal provide good feedback, but suffer high metal loss resulting in limited mode confinement (2). On the other hand, nanowire lasers on planar metal substrates achieve strong confinement with low metal loss, but the open configuration limits feedback imposing a minimum nanowire length (1). While the merits of capped and planar metallic devices remain mutually exclusive, plasmon lasers must rely on cryogenic temperatures to attain sufficient gain to combat losses. Therefore, room temperature plasmon laser operation below the diffraction limit demands low metal loss, effective cavity feedback and high gain; all within a single nanoscale device.We report here a room temperature semiconductor plasmon laser with both strong cavity feedback and λ/20 optical confinement. The device consists of a 45 nm thick, 1 μm length single crystal Cadmium Sulfide (CdS) square atop a Silver surface separated by a 5 nm thick Magnesium Fluoride gap layer, shown in Fig. 1A. We achieve strong