An Unexpected Matter

This year at the Philipps University Marburg in Germany, Mackillo Kira was among a group of physicists who unintentionally pioneered the discovery of a novel state of matter now fit to join the ranks consisting previously of solids, liquids, gases, plasma, supercritical fluids, and Bose-Einstein condensates. Known informally as a “dropleton’, or quantum droplet, this composite quasiparticle displays both liquid and particular properties. Other quasiparticles include the orbitron, a subunit of an electron, discovered in mid-2012 at Germany’s Institute for Theoretical Solid State Physics.
Says Kira, “The droplet was not predicted in advance, so its creation during the experiment came as a surprise.” The novel quasiparticles were observed when physicists directed energy pulses from a laser at a quantity of gallium arsenide. The laser created pairs of holes known as excitons in the arsenide until the exciton density achieving a specified level, upon which the excitons dissolved, leaving electrons and the unpaired holes to travel cohesively. The name “dropleton” follows from the observed action of the movement of electrons and holes “flowing” around one another, as particles in a, well, droplet might.
A notable characteristic of the dropleton is that it behaves in a liquid fashion, but can exist only within other solid materials (i.e. semiconductors). This is made possible by the organization of atoms of semiconductors into discrete lattice structures, permitting clumps of electrons to travel cohesively throughout the material.
Glenn Solomon of the Joint Quantum Institute in Maryland expressed interest in the implications of the discovery of dropletons, stating that it was “new physics, not just a small detail of well-established physics,” and could assist physicists in better comprehending the quantum properties of the interactions of large numbers of particles (“many-body systems”).
Lasting for 25 picoseconds, or 2.5 × 1011 seconds, and approximately 200 nanometers in width, dropletons are as large as some of the most minute of bacteria and are regarded as among the “longest-living” of the quasiparticles, rendering them more stability for experimentation by researchers, making it not impossible, says Kira, to “really see the dropleton.”

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