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Credit: Baxley/JILA
Credit: Baxley/JILA


The states of matter; solid, liquid, gas, and plasma. Then came Bose -Einstein condensate, supercritical fluid and a few others. Time to add another state to the list; “dropletons” which are similiar  to liquids but occur under very different circumstances.

IFL Science reported that The discovery occurred when a team at the University of Colorado Joint Institute for Lab Astrophysics were focusing laser light on gallium arsenide (GaAs) to create excitons. Excitons are formed when a photon strikes a material, particularly a semiconductor. If an electron is knocked loose, or excited, it leaves what is termed an “electron hole” behind. 

According to ILF Science Graduate student Andrew Almand-Hunter was forming biexcitons – two excitons that behave like a molecule, by focusing the laser to a dot 100nm across and leaving it on for shorter and shorter fractions of a second.
“But the experiment didn’t behave at all in the way we expected,” Almand-Hunter said. When the pulses were lasting less than 100 millionths of a second exciton density reached a critical threshold. “We expected to see the energy of the biexcitons increase as the laser generated more electrons and holes. But, what we saw when we did the experiment was that the energy actually decreased!”

According to Scientific American the quasiparticles can form in semiconductors because semiconductors’ atoms are organized into a lattice by the bonding of their valence (outer shell) electrons. This arrangement allows a conglomeration of electrons and holes to effectively travel though the material as a coherent entity.

Dropletons last for only about 25 picoseconds (trillionths of a second), but that makes them relatively long-lived for complex quasiparticles. They are stable enough, for example, to allow scientists to experiment on them. Such experiments, because of dropletons’ size, could provide an intriguing probe into the quantum interactions of light and matter. At around 200 nanometers wide, they are more than 10 times larger than single exciton pairs and about as big as some of the smallest bacteria. The laser light used to excite the material in the experiment had a wavelength of 800 nanometers, which is not too much larger than the quasiparticles themselves.

Read more at Scientific American and IFL Science.