In both the new reports, however, the experimenters used means other than extreme cold to make the condensates. The starting materials, which had not previously been formed into condensates, were what physicists call quasiparticles. According to Sergej O. Demokritov of the University of Münster in Germany, quasiparticles are ephemeral energy excitations that come and go inside solid materials, somewhat like the crests of waves in an ocean do. Quasiparticles can collide and exchange velocity as billiard balls do and otherwise behave fleetingly like standard particles, he notes.
In the set of experiments conducted at room temperature, Demokritov and his colleagues zapped a thin film of the magnetic compound yttrium iron garnet that they had placed in a device akin to a microwave oven. The treatment boosted the film's population of quasiparticles known as magnons.
In the other, much lower-temperature experiments, physicist Benoît Deveaud-Plédran of the École Polytechnique Fédérale de Lausanne in Switzerland and his colleagues fired a laser at a microstructure made of the semiconductor cadmium telluride. In the material, the procedure produced quasiparticles called exciton polaritons, which form when photons of light and electrons collide.
In each experimental run, the elevated quasiparticle densities caused the wavelike entities to overlap and form condensates, the investigators say.
In a commentary published with the reports, Snoke says that the magnon-making study, while promising, lacks firm evidence that the magnetic waves exactly match each other as they should in a condensate.
Demokritov says that in additional experiments, his team has demonstrated that the waves match.
Quasiparticles are excited states of matter that propagate as waves analogously to a particle in a vacuum. The simplest quasiparticle is the phonon, or quantized sound wave, in a crystal. The "exciton-polariton" is an excitation of the electrons of the crystal coupled with a light wave. ( There are also phonon-polaritons, where lower frequency light interacts with the atoms of the crystal ) cf. Wikipedia!
With each other and with other particles.