Excitons Condensed Into Matter Wave
Key to the operation of computers and many other electronics are semiconductors. The atoms of these materials normally hold onto their electrons, but if enough energy is fed to them, an electron can be popped up to a conducting energy band. When this happens a positively charged hole is left where the electron was, and the movement of the hole is just as important to the operation of semiconductors as the movement of the electron. Understanding these holes and excitons, the quasiparticles that represents an electron-hole pair, has been difficult though because of how short lived excitons are. Researchers at the University of California, San Diego have taken a big step toward studying excitons by successfully trapping them in a condensate.
Excitons are easily created by firing a laser at a semiconductor. Normally however the electron and hole recombine very quickly, which the researchers overcame by using a laser capable of flinging the two quanta far away from each other. To keep the exciton from recombining, the researchers used coupled quantum wells, which trap the electrons and holes in different layers of an alloy. Using an electrostatic trap, the researchers then grabbed the excitons at the end of an electrode that was cooled to just 50 milli-Kelvin, or 0.05 K. At this temperature the waveform of the trapped excitons cohered and condensed into a single matter wave.
When condensed like this, even though there are multiple particles involved, they all act as one. This has been achieved before as atoms were chilled into Bose-Einstein condensates, but this is the first time any subatomic particle has formed such a condensate. While the potential of repeating this experiment with other subatomic particles is something many researchers are going to be interested in, the ability to carefully study excitons is sure to excite researchers as well.