Particle physics experiments

Experiments reveal the formation of new states of matter

The basic principle of superconductivity is the formation of electron pairs. By pairing, electrons can overcome any electrical resistance, making the material a superconductor. In simple terms, no pairs of electrons, no superconductivity.

Can electrons condense into quartets?

A new study has found the answer, suggesting they can. A physicist from the KTH Royal Institute of Technology offered the first experimental evidence for electron quadruplets and discovered a new state of matter. The study also unveils the mechanism by which this state of matter occurs.

Physicist Egor Babaev of the Royal KTH Institute of Technology and his collaborators presented the evidence for the quadrupling of fermions in the iron-based material, Ba1 − xKxFe2As2. The results follow nearly 20 years after Babaev first predicted this phenomenon and eight years after the publication of an article indicating that it could occur in the material.

In recent years, the theoretical idea of ​​four-fermion condensates has become widely accepted.

Forming a quadrupling state of fermions requires something that prevents the condensation of pairs and prevents their flow without resistance. At the same time, it should allow the condensation of four-electron composites.

The Bardeen-Cooper-Schrieffer theory does not allow such behavior.

In 2018, Babaev’s experimental collaborator at the Technische Universtät Dresden, Vadim Grinenko, discovered the first signs of a quadrupling of the fermion condensate. The discovery called into question years of widespread scientific agreement.

After carrying out experiments and investigations in the laboratory for three years, Babaev was able to validate the results.

Babaev says that “The key among the observations made is that the fermionic quadruple condensates spontaneously break the time inversion symmetry. In physics, time reversal symmetry is a mathematical operation of replacing the expression of time with its negative in formulas or equations so that they describe an event in which time goes back, or all movements are reversed. .

“If you reverse the direction of time, the fundamental laws of physics still hold. This also applies to typical superconductors: if the arrow of time is reversed, a typical superconductor would still be the same superconducting state.

“However, in the case of a four-fermion condensate that we are reporting, the time reversal puts it in a different state.”

“It will probably take many years of research to fully understand this condition. The experiments open up several new questions, revealing several other unusual properties associated with its reaction to thermal gradients, magnetic fields and ultrasound that still need to be better understood.

Journal reference:
  1. Vadim Grinenko, State with spontaneously shattered time inversion symmetry above the superconducting phase transition, Nature Physics (2021). DOI: 10.1038 / s41567-021-01350-9

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