Physicists Have Created a New State of Matter. With Four Electrons?

And it could open an entire new field in physics.
Loukia Papadopoulos
The iron-based superconductor material, Ba1−xKxFe2As2.Vadim Grinenko, Federico Caglieris/KTH Royal Institute of Technology

Twenty years ago, scientists first predicted electron quadruplets. Now, KTH Professor Egor Babaev, with the aid of international collaborators, has revealed evidence of fermion quadrupling in a series of experimental measurements on the iron-based material, Ba1−xKxFe2As2.

This is the first-ever experimental evidence of this quadrupling effect and the mechanism by which this state of matter occurs.

"It will probably take many years of research to fully understand this state," Babaev said in a statement. "The experiments open up a number of new questions, revealing a number of other unusual properties associated with its reaction to thermal gradients, magnetic fields, and ultrasound that still have to be better understood."

Electron pairings enable the quantum state of superconductivity. This state occurs within a material as a result of two electrons bonding rather than repelling each other.

These pairings are referred to as Cooper pairs and are basically created through the "opposites that attract" principle. Under normal circumstances, two electrons — which are negatively charged subatomic particles — would strongly repel each other.

But at low temperatures in a crystal, currents of electron pairs no longer scatter from defects and obstacles and a conductor can lose all electrical resistance, becoming a new state of matter: a superconductor.

In recent years, we have seen the idea of four-fermion condensates becoming slowly broadly accepted.

Babaev's experimental collaborator at Technische Universtät Dresden, Vadim Grinenko, found in 2018 the first signs of a fermion quadrupling condensate, going against years of prevalent scientific agreement.

So naturally, the observation had to be followed by three years of experimentation and investigation in order to validate the finding. Babaev also added that fermionic quadruple condensates spontaneously break time-reversal symmetry. 

He further said that that also holds for typical superconductors: if the arrow of time is reversed, a typical superconductor would still be in the same superconducting state. "However, in the case of a four-fermion condensate that we report, the time reversal puts it in a different state," he concluded.

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