Electron Quadruplets Suggest New Physics, Applications

Novel electron pairs of pairs may be commonplace and even find use in sensors

2 min read
Close-up of gold wires attached to a yellow material with a strip of grey and blue blobs

The iron-based superconductor material, Ba1−xKxFe2As2, is mounted for experimental measurements.

Vadim Grinenko and Federico Caglieris

Experiments have now revealed a new state of matter—electron quadruplets—which researchers suggest may one day lead to new kinds of sensors as well as untold other novel applications.

The new discovery invites comparisons to the mechanisms underlying superconductors, materials that conduct electricity without dissipating energy. Superconductivity relies on electrons not repelling each other as they do in ordinary materials, but instead forming weakly bonded duos known as Cooper pairs, which can flow with zero resistance.

Nearly 20 years ago, study senior author Egor Babaev, a theoretical physicist now at the KTH Royal Institute of Technology in Stockholm, Sweden, and his colleagues suggested it was also possible for electrons to form quartets. They later predicted electron quadruplets could form within materials such as barium potassium iron arsenide.

"This is a new state of matter, that we believe is no less interesting than superconductivity and superfluidity," Babaev says.

The researchers suggested these "quartic phases" could arise before materials achieved superconducting states, when temperature and other conditions prevented the condensation of Cooper pairs but allowed the formation of electron foursomes.

"At that time our theoretical works were considered something impossible by most people and did not have any resonance in the community," Babaev says.

The first experimental glimpses of this novel state happened accidentally in 2017, when study lead author Vadim Grinenko, an experimental physicist at the Technical University of Dresden in Germany, and his colleagues discovered superconductivity in barium potassium iron arsenide. They discovered thermal, electrical and magnetic anomalies they could not account for even though "a great effort was taken to make better measurements to get rid of that impossible effect," Grinenko recalls.

After Babaev and Grinenko met by chance at a 2018 conference in Stockholm, Babaev realized Grinenko potentially discovered electron quadruplets. Substantiating their findings enough for a scientific journal to accept took more than three more years of research, they recall.

"In our work, we report the first experimental realization of the quadrupling state," Grinenko says.

One exotic property of the quartic state is "there are spontaneously forming flows that produce local magnetic fields," Babaev says. Such spontaneous currents and magnetic fields are not seen with Cooper pairs and typical superconductors, he notes.

It remains uncertain what applications this new discovery might hold, if any. However, the ways in which quartets of electrons can move in relation to each other can be significantly more complex than seen with pairs of electrons, so "we expect that a lot of new physics will be revealed, inevitably resulting in new applications," Babaev says. Grinenko does add the unconventional properties that appear with electron quartets could potentially find use in sensors.

The researchers predict there are many more materials where electron quadruplets can form. "Detection of this state is subtle and requires complex studies, and therefore it may have been overlooked in some already known materials," Grinenko says. He adds that electron quadruplets could be a quite general phenomenon, especially in two-dimensional films.

The scientists detailed their findings online Oct. 18 in the journal Nature Physics.

The Conversation (1)
FB TS 30 Oct, 2021

Is there really any concrete evidence that Cooper pairs actually exists?Why that theory cannot explain all superconductors, if superconductivity really happens that way?What if, (all kinds of) superconductivity is just electrons creating a (2D/3D) superfluid state?

Can This DIY Rocket Program Send an Astronaut to Space?

Copenhagen Suborbitals is crowdfunding its crewed rocket

15 min read
Five people stand in front of two tall rockets. Some of the people are wearing space suits and holding helmets, others are holding welding equipment.

Copenhagen Suborbitals volunteers are building a crewed rocket on nights and weekends. The team includes [from left] Mads Stenfatt, Martin Hedegaard Petersen, Jørgen Skyt, Carsten Olsen, and Anna Olsen.

Mads Stenfatt

It was one of the prettiest sights I have ever seen: our homemade rocket floating down from the sky, slowed by a white-and-orange parachute that I had worked on during many nights at the dining room table. The 6.7-meter-tall Nexø II rocket was powered by a bipropellant engine designed and constructed by the Copenhagen Suborbitals team. The engine mixed ethanol and liquid oxygen together to produce a thrust of 5 kilonewtons, and the rocket soared to a height of 6,500 meters. Even more important, it came back down in one piece.

That successful mission in August 2018 was a huge step toward our goal of sending an amateur astronaut to the edge of space aboard one of our DIY rockets. We're now building the Spica rocket to fulfill that mission, and we hope to launch a crewed rocket about 10 years from now.

Copenhagen Suborbitals is the world's only crowdsourced crewed spaceflight program, funded to the tune of almost US $100,000 per year by hundreds of generous donors around the world. Our project is staffed by a motley crew of volunteers who have a wide variety of day jobs. We have plenty of engineers, as well as people like me, a pricing manager with a skydiving hobby. I'm also one of three candidates for the astronaut position.

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