Researchers discovered a new semiconductor quasiparticle using an ultrafast laser.
A quasiparticle is a "handful of smaller particles that briefly condense into a liquid-like droplet," a National Institute of Standards and Technology (NIST) news release reported. These smaller particles can be spawned inside a solid material; and researchers can predict how they'll behave.
An example of this phenomenon is "exciton," which is a pairing of an electron and a hole (an empty space where an electron should be).
The newly-discovered quasiparticle is a never before seen arrangement of these electrons and holes. The researchers dubbed it a "quantum droplet" because it possesses "quantum characteristics" as well as energy levels; it also shares some characteristics with a liquid, such as the fact that it can form ripples. The droplet differs from liquids such as water because it has a "finite" size.
Even though the droplet only exists for 25 picoseconds (trillionths of a second) the researchers were still able to see how light interacted with the matter.
"Electron-hole droplets are known in semiconductors, but they usually contain thousands to millions of electrons and holes," JILA physicist Steven Cundiff, who studies the properties of cutting-edge lasers and what they reveal about matter, said in the news release in reference to a droplet with about five holes. "Regarding practical benefits, nobody is going to build a quantum droplet widget. But this does have indirect benefits in terms of improving our understanding of how electrons interact in various situations, including in optoelectronic devices."
The team created these droplets using a "gallium-arsenide semiconductor with an ultrafast red laser emitting about 100 million pulses per second," the news release reported. The pulses would form excitons.
As the laser pulse increases more holes are created, eventually creating a quantum droplet when a certain density has been reached. When this occurs the pairing disappears and and the pairings fill in the holes, creating a neutral droplet.
"The droplets are like bubbles held together briefly by pressure from the surrounding plasma," the news release reported.
The researchers found they could "tap into" each energy level by correlating the pulses with the hole and electron pairings. The team plans to use these droplets to study reactions between matter and light in the future.
