Discovery of quantum behavior in isolators indicates possible new particles

Discovery of quantum behavior in isolators indicates possible new particles

A team led by Princeton physicists discovered a surprising quantum phenomenon in an atom-thin insulator made of tungsten ditelluride. The results indicate the formation of completely new types of quantum phases that were previously hidden in insulators. Credit: Kai Fu for Wu Lab, Princeton University

In a surprising discovery, Princeton physicists observed an unexpected quantum behavior in an insulator made of a material called tungsten ditelluride. This phenomenon, known as quantum oscillation, is usually observed in metals rather than insulators, and its discovery offers new insights into our understanding of the quantum world. The findings also indicate the existence of a completely new kind of quantum particle.

The discovery disputes a long-standing distinction between metals and insulators, because in the established quantum theory of materials, insulators are not thought to be capable of experiencing quantum changes.

“If our interpretations are correct, we see a fundamentally new form of quantum matter,” said Sanfeng Wu, assistant professor of physics at Princeton University, and the senior author of a recent article in Earth which sets out this new discovery. “We now imagine a whole new quantum world hidden in insulators. It is possible that we have simply missed it over the past few decades.”

The observation of quantum eruptions has long been considered a feature of the difference between metals and insulators. In metals, electrons are very mobile and resistance – the resistance to electrical conduction – is weak. Nearly a century ago, researchers observed that a magnetic field, coupled with very low temperatures, could cause electrons to shift from a ‘classical’ state to a quantum state, causing oscillations in the metal’s resistance. In insulators, on the other hand, electrons cannot move and the materials have a very high resistance, so quantum changes are not expected to occur regardless of the strength of the magnetic field applied.

The discovery was made when the researchers studied a material called tungsten ditelluride, which they made into a two-dimensional material. They prepared the material using standard adhesive tape to increasingly peel, or “shave”, the layers down to the so-called monolayer – a single atom-thin layer. Thick tungsten ditelluride behaves like a metal. But once it is converted into a monolayer, it becomes a very strong insulator.

“This material has very special quantum properties,” Wu said.

The researchers then measured the resistance of the monolayer tungsten ditelluride under magnetic fields. To their surprise, the resistance of the insulator, despite being quite large, began to fluctuate as the magnetic field increased, indicating the shift to a quantum state. In fact, the material – a very strong insulator – exhibits the most remarkable quantitative property of a metal.

“It was a total surprise,” Wu said. “We asked ourselves, ‘What’s going on here?’ We do not quite understand it yet. ‘

Wu noted that there are no current theories to explain this phenomenon.

Nevertheless, Wu and his colleagues put forward a challenging hypothesis – a form of quantum matter that is neutrally charged. “Because of very strong interactions, the electrons organize themselves to produce this new kind of quantum substance,” Wu said.

But it is ultimately no longer the electrons that oscillate, Wu said. Instead, the researchers believe that new particles, which they called ‘neutral fermions’, were born from these strong interacting electrons and are responsible for creating this very remarkable quantum effect.

Fermions are a category of quantum particles that include electrons. In quantum materials, charged fermions can be negatively charged electrons or positively charged “holes” responsible for electrical conduction. Namely, if the material is an electrical insulator, these charged fermions cannot move freely. However, particles that are neutral – that is, negatively or positively charged – are theoretically possible to be present in an insulator.

“Our experimental results contradict all existing theories based on charged fermions,” said Pengjie Wang, co-author of the paper and postdoctoral research fellow, “but can be explained in the presence of charge-neutral fermions.”

The Princeton team plans further investigation into the quantum properties of tungsten ditelluride. They are particularly interested in discovering whether their hypothesis – about the existence of a new quantum particle – is valid.

“It’s just the starting point,” Wu said. “If we are right, future researchers will find other isolators with this surprising quantum property.”

Despite the novelty of the research and the preliminary interpretation of the results, Wu speculated about how this phenomenon could be used in practice.

“It is possible that neutral fermions could be used in the future to encode information that would be useful for quantum computers,” he said. “Meanwhile, however, we are still in the very early stages of understanding quantum phenomena like this, so fundamental discoveries need to be made.”


Topological insulators have lossless conductivity on the sides


More information:
Pengjie Wang et al., Landau quantization and highly mobile fermions in an insulator, Earth (2021). DOI: 10.1038 / s41586-020-03084-9

Provided by Princeton University

Quotation: Discovery of quantum behavior in isolators indicates possible new particle (2021, January 12) detected on January 12, 2021 from https://phys.org/news/2021-01-discovery-quantum-behavior-insulators-particle.html

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