Solid state, liquid state, and gas state. These are without a doubt the three best states of matter. But physicists know this, and there are quite a few others. States of matter that can be described as more exotic. For example, there is the Bose-Einstein condensate – first observed in 1938 – which corresponds to the condensation of bosons – particles like photons, for example – at the lowest energy level. Or, again, the state of superconductivity – which was discovered in 1911 – which mainly appears at a very low temperature, when the atoms that make up the material do not vibrate much.
A material placed in a superconducting state is able to conduct an electric current without resistance or energy loss. It can also literally expel a magnetic field and thus allow the positioning of high-altitude objects. This special state of matter is the result of a quantum phenomenon. In superconducting materials, electrons tend to cluster in pairs. Then their pairs interact with the atoms that surround them. They form a kind of collective wave capable of moving like a wave that is insensitive to defects in the material.
So the case of superconductivity shows that the electrons are able to condense into pairs. It made physicists wonder if these negatively charged particles could also condense into quadruplets. Already in 2004, Igor Babayev, a professor of theoretical physics, predicted this so-called quaternary effect. In 2012, he had planned that it could happen in real material. Today it is an international team, headed by the Royal Swedish Institute of Technology, which is finally providing the first experimental evidence of this new state of matter obtained on an iron-based material, Ba1-xNSxFe2as2.
Iron-based material, Ba1-xNSxFe2as2 And from it, the researchers got a new summer of a quadruple-electron material ready for these experiments. © Vadim Grinenko, Federico Caglieris, Royal Swedish Institute of Technology
From superconducting to quaternary electron
For a better understanding, let’s go back to the description of the superconducting state. A description that earned Leon Cooper – to whom we owe the name given to the electron pairs involved in the phenomenon, the Cooper pairs -, John Bardeen and John Shriver, nothing more and nothing less than the Nobel Prize in Physics in 1972. The theory we know today as BCS theory explained early in the The 1950s how electrons, at low temperature, in a crystal, can bond in pairs, both negatively charged and presumably repelled. As if opposites end up attracting each other.
But this exact theory does not allow electrons – which physicists classify as fermions – to bind together into quadruplets. Therefore, it would be really necessary for something to come along to prevent them from initially linking up in pairs. Also prevent its flow without resistance. Allowing them to condense by four.
So how did Igor Babayev’s team finally notice the quadrupling of the fermion condensation? After three years of testing and validation by several labs, there is no doubting the strength of the results. The physicist explains that the key to this new state of matter is hidden in the spontaneous collapse of the time-symmetry reversal.
The new state of matter observed by physicists at the Royal Swedish Institute of Technology can be explained by the spontaneous refraction of time-reversal symmetry. Credit: shutterstock.
Time-reversal symmetry breaking
This still requires some clarification. In the Standard Model of particle physics there are three basic symmetries. Among them, what researchers call time-reversing symmetry. A type of arithmetic operation that consists in replacing the expression for time, in formulas, with a negative. It is enough to allow them to describe an event in which time moves backwards. The basic laws of physics remain the same. The rule is valid for the superconducting state. Inverse time and superconductor will always be in the same superconducting state. But in the case of condensation of four fermions, the time reversal puts matter in a different state.
The researchers realize that it will likely take several more years of study to fully understand this new state of matter and the mechanisms that produce it. Moreover, these experiments are already raising a number of new questions regarding the unusual properties associated with the interaction of the four fermion capacitors with temperature gradients, magnetic fields or even ultrasound.
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