Tuesday , January 19 2021

Physicists find irritating hints at a “fundamentally new form of quantum matter”

Metals and insulators are the yin and yang of physics, their material properties are strictly dictated by the mobility of their electrons – metals must conduct electrons freely, while insulators hold them in place.

So when physicists at Princeton University in the United States discovered the quantum chimerism of metals bouncing inside an insulating compound, they found no explanation.

We will have to wait for further research to find out exactly what is happening. But one unpleasant possibility is that a previously unseen particle is working, which represents a neutral ground in the behavior of electrons. They call it a “neutral fermion.”

“It came as a complete surprise,” said physicist Sanfen Wu of Princeton University in the United States.

“We asked ourselves, ‘What’s going on here?’ “We don’t fully understand that yet.”

Quantum oscillations are a phenomenon in the center of the discovery. As follows from this term, it involves the oscillation back and forth of freely moving particles under certain experimental conditions.

To get a little more technical, oscillations occur when the material cools to levels where quantum behavior is easier to dominate and the magnetic field is applied and changed.

The rotation of the magnetic field up and down causes unbound charged particles, such as electrons, to slip between energy bands called Landau levels.

This is a technique commonly used to study the atomic landscape occupied by electrons in a material, especially those with metallic properties.

It is believed that insulators are a completely different kettle with fish. With their electrons, which follow strict rules of home, quantum oscillations are not a thing. At least they shouldn’t be.

The team looked at tungsten ditelluride, a strange semi-metal that acquires insulating properties when bathed in a magnetic field, and was surprised that quantum oscillations occur.

Despite the shock, they think about what might happen. Although a flowing charge would make this insulator a conductor (which is paradoxical), the presence of a “stream” of neutral particles would correspond to the insulator’s account and the quantum generator, which makes more sense.

“Our experimental results contradict all existing theories based on charged fermions, but they can be explained by the presence of charge-neutral fermions,” adds colleague Penji Wang.

The only problem is that truly neutral fermions should not exist, according to the Standard Particle Physics Model.

Fermions are particles similar to “ Lego blocks ” matter, while another type of basic particles – bosons – are charge-carrying particles.


A truly neutral particle is also its own antiparticle – and this is what we have seen in bosons, but never in fermions.

So the search for a truly neutral fermion would probably rewrite our understanding of physics, but that’s not what researchers think is happening here – instead, they believe that what they’ve found is more than a neutral quasiparticle, which is a quantum type of hybrid particle. .

To understand what a quasiparticle is, imagine particle physics as the study of music.

Fundamental particles, such as quarks and electrons, are separate tools. They form the basis of many larger particles, ranging from three-fold mountain bands, such as protons, or symphonies, as whole atoms.

Bands playing synchronously on opposite stages can even be considered as a separate event – a quasi-particle that plays as one for all purposes.

Quantum strangeness can blur the properties of electrons so that their charge particles are converted into space. In other words, some electron quasiparticles will carry some bits of an electron like its spin, but not its charge, actually creating a neutral version of itself.

What exactly the aroma of a quasiparticle acts here (if any) has not yet been developed, but researchers describe it as a completely new territory not only in experiments but also in theory.

“If our interpretations are correct, we see a fundamentally new form of quantum matter,” says Wu.

“Now we’re imagining a whole new quantum world hidden in insulators. Maybe we just missed identifying them over the last few decades.”

Neutral fermions play a potential role in increasing the stability of quantum devices, so the search for evidence of such a phenomenon would be more than academic interest, with promising practical applications.

These are still early days. But so many discoveries in science came from those timeless words: “What’s going on here?”

This study was published in Nature.

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