From NOVA: “Quasiparticle Collider Could Illuminate Mysteries of Superconductivity”



When a marten—a small, weasel-like animal—crawled inside a transformer and shut down the Large Hadron Collider, it highlighted the risks of giant science experiments. The bigger the facility, the more chances for the unexpected. Physicists use the Large Hadron Collider (LHC), a 17-mile vacuum tube buried under Geneva, Switzerland, to speed up subatomic particles to near the speed of light and smash them together.

CERN LHC Grand Tunnel
CERN LHC particles
LHC, 17 mile circular accelerator at CERN

But a team of scientists has developed a marten-proof way to collide particles—using a device the size of a tabletop.

Made up of no more than a laser and a tiny crystal, the technique studies different kinds of particles than the LHC does. They’re called quasiparticles. Quasiparticles are, in essence, disturbances that form in a material that can be classified—and modeled—as particles in their own right (even though they are not actual particles). For example, an electron quasiparticle is made up of an electron moving through a medium (in this particular study, a semiconductor crystal), plus the perturbations its negative charge causes in neighboring electrons and atomic nuclei.

A quantum dot—a nanoscale semiconductor device that tightly packs electrons and electron holes—glows a specific color when it is hit with any kind of light. The team’s new quasiparticle collider could help scientists develop more efficient light-emitting tools, beyond what the quantum dot can do.

Another example of a quasiparticle that acts as a counterpart to the electron quasiparticle is an electron hole, defined as the lack of electrons in a space surrounded by electrons. In other words, a “hole” quasiparticle is equivalent to a positively charged gap left by an electron on-the-go. So although quasiparticles a little different from what we usually think of as a particle, they’re sort of like air bubbles moving through water. Here’s Elizabeth Gibney, reporting for Nature News:

It is intuitive for physicists to think in terms of quasiparticles, in the same way that it makes sense to follow a moving bubble in water, rather than trying to chart every molecule that surrounds it, says Mackillo Kira, a physicist at the University of Marburg in Germany and co-author of a report on the quasiparticle collider, published in Nature.

Usually, the electron quasiparticle and the hole quasiparticle are bound up as a compound quasiparticle called an exciton. Their opposite charges pull them together. But with powerful laser pulses, physicists can cleave the exciton back into its component parts, which rush away from each other. Then they swing back and collide at high speed, producing light particles called photons. The physicists are able to detect the photons, which let them study what happened in the quasiparticle collision.

Those photons could hold the secrets of how quasiparticles are structured. Though they’re only around for tiny fractions of a second, quasiparticles are an important part of physics. Since quasiparticles form when light is emitted, the new technique could illuminate a way to build better solar cells or to study strange forms of matter such as superconductors, since so-called Bogoliubov quasiparticles represent half of the electron pairs required for superconductivity.

See the full article here .

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