A new quasiparticle has been discovered, according to a report published in Science on Thursday. The new phenomenon, called a "plasmaron," was found in a sample of doped graphene, where it appeared courtesy of the material's unusual arrangement of electrons in its electron cloud. Because the behavior of the quasiparticle is different from that of its individual components, researchers should be able to use this new knowledge to make better predictions of the atomic and molecular states present in graphene, and keep watch for the appearance of plasmarons in similar materials.
A quasiparticle is not a sort-of particle, as the name implies, but usually represents a combination of a bulk effect and a material. For example, an electron is only a particle, but an electron that blocks the attraction between another electron and a proton could act as a quasiparticle. A quasiparticle can also be purely effect, like plasmons, which are quantum packets of excitation in the electrons in a metal. To find quasiparticles, researchers often have to be able to isolate a single particle behaving a particular way—not always an easy task.
When these particular researchers looked at graphene doped with potassium and its band structure (the energies that electrons can occupy), they found one spot where holes left by electrons exhibited unusual behavior—their movement couldn't be described by the normal set of rules.
They realized that the intersection of charge bands caused the holes to have greater binding energy than usual, and that these are actually able to exert plasmon effects on their environment. The combination meant they had a new quasiparticle on their hands: the plasmaron.
The appearance of the quasiparticle seems like a highly specialized case, since it was found in a specific material prepared a special way. Still, knowing its behavior and weird manipulation of energy will allow researchers to account for it more fully when modeling uses of graphene, as well as look for it to crop up in similar electron-hole situations.