In a surprising discovery, Princeton physicists observed an unexpected quantum behavior in insulators made of a material known as tungsten diethyluride. This phenomenon, known as quantum oscillation, is generally observed in metals rather than insulators, and the discovery offers new insights into our understanding of the quantum world. The discovery also indicates the existence of an entirely new type of quantum particle.
The discovery challenges the long-standing distinction between metals and insulators because, in the established quantum material theory, insulators were not thought to be able to experience quantum oscillations.
“If our interpretation is correct, we can see a fundamentally new form of quantum matter,”; said Sanfeng Wu, assistant professor of physics at the University of California. Princeton University And senior author of a recent article in nature This new discovery details “We are now imagining a whole new quantum world hidden in insulators. It is possible that we have missed out on identifying over the past several decades. ”
The observation of quantum oscillations has long been a hallmark of the difference between metals and insulators. In metals, electrons are highly mobile and resistance – resistance to conductivity – soft. Nearly a century ago, researchers observed that magnetic fields, coupled with extremely low temperatures, can cause electrons to go from “classical” to “classical” states. Quantum induces oscillations in the metal’s resistance. In an insulator, on the contrary, electrons are immobile and the material has a very high resistance, so this type of quantum oscillation is not expected to occur regardless of the strength of the magnetic field.
The breakthrough came when researchers were studying a material called tungsten diethyluride, which makes it a two-dimensional material. They prepare the material using a standard scotch tape to scrub more or “shave” down to a layer called a monolayer – a single disc. atom– Thick tungsten diethyluride layer acts like metal. But when converted to monolayer, it becomes a very strong insulator.
“This material has a lot of special quantum properties,” said Wu.
The researchers then set out to measure the resistance of a single tungsten diethyluride under a magnetic field. To my surprise, the insulation resistance, although quite large. But it starts to vibrate as the magnetic field increases, indicating a transition to a quantum state. In fact, this very strong insulator material is exhibiting some of the most amazing quantum properties of metals.
“This is a huge surprise,” said Wu. ‘What happened here?’ We don’t fully understand.
Wu noted that there is no current theory to explain this phenomenon.
However, Wu and his colleagues made a provocative hypothesis, a form of neutral-charged quantum matter. “Due to their very strong interactions, electrons organize themselves to form quantum matter. This new kind, ”Wu said.
But in the end, it was no longer the electrons that were vibrating, Wu said. But the researchers believe the new particles, which they dubbed The “neutral fermion” is formed by these strongly interacting electrons and is responsible for producing remarkable quantum effects.
Fermions are a category of quantum particles that combine electrons. In quantum materials, charged fermions can be negatively charged electrons or positively charged “holes” responsible for electrical conductivity. In other words, if the material is electrically insulated, these electrically charged ferrules cannot move independently. However, a neutral particle, that is, theoretically has no negative or positively charged ions, it is possible to exist and move in an insulation.
“Our results contradict all existing theories based on charged fermions,” said Pengjie Wang, co-author of the paper and a postdoctoral co-author, “but this can only be explained when there is an active fermion. Has a neutral charge “
The Princeton team plans further investigations into the quantum properties of tungsten diethyluride. They were especially interested in discovering whether their hypothesis about the existence of new quantum particles was correct.
“This is just the beginning,” Wu said. “If we’re right, future researchers will find other insulators with this surprising quantum feature.”
Despite the new research and interpretation of the preliminary results, Wu speculated on how the phenomenon would be practical.
It is possible that in the future neutral fermions for encoding information would be useful. Quantum computer, “He said.” In the meantime, we are still in the early stages of understanding quantum phenomena, so a fundamental discovery is required. “
Reference: “Determination of Landau and Highly Mobile Fermion in Insulators” 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 first co-author Guo Yu, a graduate student in electrical engineering, and Yanyu Jia, a physics graduate student. Princeton’s other key contributor was Leslie Schoop, assistant professor of chemistry. Robert Kava, Russell Welman Moore Professor of Chemistry; Michael Onyszczak, graduate student in physics; And three former postdoctoral fellows, Shiming Lei, Sebastian Klemenz, and F. Alexandre Cevallos, the 2018 Princeton alumni.Kenji Watanabe and Takashi Taniguchi from the National Institute for Material Science in Japan contributed information. with
“Landau quantification and movable fermion in insulation” 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 are published in the journal Jan. 4. nature (DOI: 10.1038 / s41586-020-03084-9)
This work was funded primarily by the National Science Foundation (NSF) through the Princeton University Materials Research Science and Engineering Center (DMR-1420541 and DMR-2011750) and the CAREER award (DMR-1942942) .Early measurements were performed at the room. National High Magnetic Field Operations, supported by the NSF Cooperative Agreement (DMR-1644779) and the state of Florida. Further support comes from the Elemental Strategy Initiative run by the Japanese Ministry of Education, Culture, Sports, Science and Technology. (JPMXP0112101001), Japan Science and Technology Agency’s KAKENHI Project (JP20H00354) and the Japan Science and Technology Agency’s CREST Program (JPMJCR15F3), additional support is from the US Army Research Office Multidisciplinary University Research Initiative on Topological Insulators (W911NF1210461), Arnold and Mabel. Beckman Foundation, through the Beckman Young Investigator Scholarship and the Gordon and Betty Moore Foundation (GBMF9064).