Spotted: Ghost surface polaritons
A type of hybrid light-matter quasiparticle seen for the first time.
For the first time, an international research team has demonstrated the existence of ghost hyperbolic surface polaritons, and it’s just about as mind-bending as it sounds.
“Polaritonics is the science and technology of exploiting strong interactions of light with matter, and it has revolutionised optical sciences in the past few years,” explains Andrea Alù, co-author of the new study from the City University of New York.
“Our discovery is the latest example of the exciting science and surprising physics that can emerge from exploring polaritons in conventional materials like calcite.”
Polaritons fall under the classification of “quasiparticles”, which are disturbances within a medium that act like particles, even if they aren’t really one, and so can be treated as particle-like.
Quasiparticles are an important concept in condensed matter physics because they play a role in the properties of matter.
The study, published in Nature, observed hyperbolic polaritons at the surface of bulk crystals of a common material, calcite.
The team were exploring how light interacted with calcite, and found unexpected responses from infrared polaritons. They demonstrated that calcite can support ghost polariton surface waves, which have features (including complex, out-of-plane momentum) unlike any other observed surface polariton to date.
These findings may be able to help researchers better control and enhance light-matter interactions at the nanoscale, which is essential in technologies across sensing, biomolecular and chemical diagnosis, signal processing, energy harvesting and more.