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

The discovery challenges a long-held distinction between metals and insulators, because in the established quantum theory of materials, insulators were not thought to be able to experience quantum oscillations.

If our interpretations are correct, we are seeing a fundamentally new form of quantum matter, said Sanfeng Wu, assistant professor of physics at Princeton University and the senior author of a recent paper in Nature detailing this new discovery. We are now imagining a wholly new quantum world hidden in insulators. Its possible that we simply missed identifying them over the last several decades.

The observation of quantum oscillations has long been considered a hallmark of the difference between metals and insulators. In metals, electrons are highly mobile, and resistivity the resistance to electrical conduction is weak. Nearly a century ago, researchers observed that a magnetic field, coupled with very low temperatures, can cause electrons to shift from a classical state to a quantum state, causing oscillations in the metals resistivity. In insulators, by contrast, electrons cannot move and the materials have very high resistivity, so quantum oscillations of this sort are not expected to occur, no matter the strength of magnetic field applied.

The discovery was made when the researchers were studying a material called tungsten ditelluride, which they made into a two-dimensional material. They prepared the material by using standard scotch tape to increasingly exfoliate, or shave, the layers down to what is called a monolayer a single atom-thin layer. Thick tungsten ditelluride behaves like a metal. But once it is converted to a monolayer, it becomes a very strong insulator.

This material has a lot of special quantum properties, Wu said.

The researchers then set about measuring the resistivity of the monolayer tungsten ditelluride under magnetic fields. To their surprise, the resistivity of the insulator, despite being quite large, began to oscillate as the magnetic field was increased, indicating the shift into a quantum state. In effect, the material a very strong insulator was exhibiting the most remarkable quantum property of a metal.

This came as a complete surprise, Wu said. We asked ourselves, Whats going on here? We dont fully understand it yet.

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

Nonetheless, Wu and his colleagues have put forward a provocative hypothesis a form of quantum matter that is neutrally charged. Because of very strong interactions, the electrons are organizing themselves to produce this new kind of quantum matter, Wu said.

But it is ultimately no longer the electrons that are oscillating, said Wu. Instead, the researchers believe that new particles, which they have dubbed neutral fermions, are born out of these strongly interacting electrons and are responsible for creating this highly 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 that are responsible for the electrical conduction. Namely, if the material is an electrical insulator, these charged fermions cant move freely. However, particles that are neutral that is, neither negatively nor positively charged are theoretically possible to be present and mobile in an insulator.

Our experimental results conflict with all existing theories based on charged fermions, said Pengjie Wang, co-first author on the paper and postdoctoral research associate, but could 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.

This is only the starting point, Wu said. If were correct, future researchers will find other insulators with this surprising quantum property.

Despite the newness of the research and the tentative interpretation of the results, Wu speculated about how this phenomenon could be put to practical use.

Its possible that neutral fermions could be used in the future for encoding information that would be useful in quantum computing, he said. In the meantime, though, were still in the very early stages of understanding quantum phenomena like this, so fundamental discoveries have to be made.

Reference: Landau quantization and highly mobile fermions in an insulator by Pengjie Wang, Guo Yu, Yanyu Jia, Michael Onyszczak, F. Alexandre Cevallos, Shiming Lei, Sebastian Klemenz, Kenji Watanabe, Takashi Taniguchi, Robert J. Cava, Leslie M. Schoop and Sanfeng Wu, Nature.DOI: 10.1038/s41586-020-03084-9

In addition to Wu and Wang, the team included co-first authors Guo Yu, a graduate student in electrical engineering, and Yanyu Jia, a graduate student in physics. Other key Princeton contributors were Leslie Schoop, assistant professor of chemistry; Robert Cava, the Russell Wellman Moore Professor of Chemistry; Michael Onyszczak, a physics graduate student; and three former postdoctoral research associates: Shiming Lei, Sebastian Klemenz and F. Alexandre Cevallos, who is also a 2018 Princeton Ph.D. alumnus. Kenji Watanabe and Takashi Taniguchi of the National Institute for Material Science in Japan also contributed.

Landau quantization and highly mobile fermions in an insulator, by Pengjie Wang, Guo Yu, Yanyu Jia, Michael Onyszczak, F. Alexandre Cevallos, Shiming Lei, Sebastian Klemenz, Kenji Watanabe, Takashi Taniguchi, Robert J. Cava, Leslie M. Schoop, and Sanfeng Wu, was published Jan. 4 in the journal Nature (DOI: 10.1038/s41586-020-03084-9).

This work was primarily supported by the National Science Foundation (NSF) through the Princeton University Materials Research Science and Engineering Center (DMR-1420541 and DMR-2011750) and a CAREER award (DMR-1942942). Early measurements were performed at the National High Magnetic Field Laboratory, which is supported by an NSF Cooperative Agreement (DMR-1644779), and the State of Florida. Additional support came from the Elemental Strategy Initiative conducted by the Ministry of Education, Culture, Sports, Science and Technology of Japan (JPMXP0112101001), the Japan Society for the Promotion of Sciences KAKENHI program (JP20H00354) and the Japan Science and Technology Agencys CREST program (JPMJCR15F3). Further support came from the U.S. Army Research Office Multidisciplinary University Research Initiative on Topological Insulators (W911NF1210461), the Arnold and Mabel Beckman Foundation through a Beckman Young Investigator grant, and the Gordon and Betty Moore Foundation (GBMF9064).

Original post:

Surprising Discovery of Unexpected Quantum Behavior in Insulators Suggests Existence of Entirely New Type of Particle - SciTechDaily

Albert Einstein's theory of general relativity profoundly changed our thinking about fundamental concepts in physics, such as space and time. But it also left us with some deep mysteries.

One was black holes, which were only unequivocally detected over the past few years. Another was "wormholes" bridges connecting different points in spacetime, in theory providing shortcuts for space travellers.

Wormholes are still in the realm of the imagination. But some scientists think we will soon be able to find them, too. Over the past few months, several new studies have suggested intriguing ways forward.

Black holes and wormholes are special types of solutions to Einstein's equations, arising when the structure of spacetime is strongly bent by gravity. For example, when matter is extremely dense, the fabric of spacetime can become so curved that not even light can escape. This is a black hole.

As the theory allows the fabric of spacetime to be stretched and bent, one can imagine all sorts of possible configurations.

In 1935, Einstein and physicist Nathan Rosen described how two sheets of spacetime can be joined together, creating a bridge between two universes. This is one kind of wormhole and since then many others have been imagined.

Some wormholes may be "traversable", meaning humans may be able to travel through them. For that though, they would need to be sufficiently large and kept open against the force of gravity, which tries to close them. To push spacetime outward in this way would require huge amounts of "negative energy".

Sounds like sci-fi? We know that negative energy exists, small amounts have already been produced in the lab. We also know that negative energy is behind the Universe's accelerated expansion.

So nature may have found a way to make wormholes.

How can we ever prove that wormholes exist? In a new paper, published in the Monthly Notices of the Royal Society, Russian astronomers suggest they may exist at the centre of some very bright galaxies, and propose some observations to find them.

This is based on what would happen if matter coming out of one side of the wormhole collided with matter that was falling in. The calculations show that the crash would result in a spectacular display of gamma rays that we could try to observe with telescopes.

This radiation could be the key to differentiating between a wormhole and a black hole, previously assumed to be indistinguishable from the outside. But black holes should produce fewer gamma rays and eject them in a jet, while radiation produced via a wormhole would be confined to a giant sphere.

Although the kind of wormhole considered in this study is traversable, it would not make for a pleasant trip. Because it would be so close to the centre of an active galaxy, the high temperatures would burn everything to a crisp.

But this wouldn't be the case for all wormholes, such as those further from the galactic centre.

The idea that galaxies can harbour wormholes at their centres is not new. Take the case of the supermassive black hole at the heart of the Milky Way. This was discovered by painstakingly tracking of the orbits of the stars near the black hole, a major achievement which was awarded the Nobel Prize in Physics in 2020.

But one recent paper has suggested this gravitational pull may instead be caused by a wormhole.

Unlike a black hole, a wormhole may "leak" some gravity from the objects located on the other side. This spooky gravitational action would add a tiny kick to the motions of stars near the galactic centre. According to this study, the specific effect should be measurable in observations in the near future, once the sensitivity of our instruments gets a little bit more advanced.

Coincidentally, yet another recent study has reported the discovery of some "odd radio circles" in the sky. These circles are strange because they are enormous and yet not associated with any visible object. For now, they defy any conventional explanation, so wormholes have been advanced as a possible cause.

Wormholes hold a strong grip on our collective imagination. In a way, they are a delightful form of escapism. Unlike black holes which are a bit frightening as they trap everything that ventures in, wormholes may allow us to travel to faraway places faster than the speed of light.

They may in fact even be time machines, providing a way to travel backwards as suggested by the late Stephen Hawking in his final book.

Wormholes also crop up in quantum physics, which rules the world of atoms and particles. According to quantum mechanics, particles can pop out of empty space, only to disappear a moment later.

This has been seen in countless experiments. And if particles can be created, why not wormholes?

Physicists believe wormholes may have formed in the early Universe from a foam of quantum particles popping in and out of existence. Some of these "primordial wormholes" may still be around today.

Recent experiments on "quantum teleportation" a "disembodied" transfer of quantum information from one location to another have turned out to work in an eerily similar way to two black holes connected through a wormhole.

These experiments appear to solve the "quantum information paradox", which suggests physical information could permanently disappear in a black hole. But they also reveal a deep connection between the notoriously incompatible theories of quantum physics and gravity with wormholes being relevant to both which may be instrumental in the construction of a "theory of everything".

The fact that wormholes play a role in these fascinating developments is unlikely to go unnoticed. We may not have seen them, but they could certainly be out there. They may even help us understand some of the deepest cosmic mysteries, such as whether our Universe is the only one.

Andreea Font, Senior Lecturer of Astrophysics, Liverpool John Moores University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read more from the original source:

If Wormholes Are Lurking in Our Universe, This Is How We Could Find Them - ScienceAlert