A DROPLET of "electric liquid" can be squeezed from a semiconductor by shooting it with lasers. The quantum droplet is a new kind of particle that could help study how light and matter interact.
As electrons flow through a semiconductor, they leave behind "holes" – the absence of an electron. Holes are considered a kind of particle in their own right. Electrons can bind to holes, much as how an electron circles a proton in a hydrogen atom. Electron-hole pairs are called excitons, and they in turn can group to create quasi-molecules called polyexcitons.
Mackillo Kira at the University of Marburg, Germany, and his team have taken this quasi-chemistry a step further. They found that certain collections of electrons and holes can have liquid-like properties, creating a quasi-particle they call the dropleton. "Our dropleton discovery adds a new element to the 'periodic table' of quasi-particles," says Kira.
The team produced the dropletons by firing a laser at a semiconductor, creating a large number of unbound electrons and holes. When the laser has particular quantum properties, groups of these particles behave like liquids. Rather than binding in pairs, the electrons form circular waves around the holes, which are spaced similarly to how atoms are arranged in a liquid. Four electrons and four holes are enough to make a dropleton, and the team made them with as many as 14 of each.
They last for just 25 trillionths of a second, but that should be long enough to study them and their potential use in technology.
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