From The University of Colorado-Boulder Via “phys.org” : “Physicists probe ‘astonishing’ morphing properties of honeycomb-like material”
From The University of Colorado-Boulder
Via
10.12.22
By exposing a honeycomb-like material with a specific kind of magnetic field, yellow arrow, researchers can create order among the loop currents, light blue, within that material. Electrons, in green, can then pass through the material much more easily. Credit: The DOE’s Oak Ridge National Laboratory.
A series of buzzing, bee-like “loop-currents” could explain a recently discovered, never-before-seen phenomenon in a type of quantum material. The findings from researchers at the University of Colorado Boulder may one day help engineers to develop new kinds of devices, such as quantum sensors or the quantum equivalent of computer memory storage devices.
The quantum material in question is known by the chemical formula Mn3Si2Te6. But you could also call it “honeycomb” because its manganese and tellurium atoms form a network of interlocking octahedra that look like the cells in a beehive.
Physicist Gang Cao and his colleagues at CU Boulder synthesized this molecular beehive in their lab in 2020, and they were in for a surprise: Under most circumstances, the material behaved a lot like an insulator. In other words, it didn’t allow electric currents to pass through it easily. When they exposed the honeycomb to magnetic fields in a certain way, however, it suddenly became millions of times less resistant to currents. It was almost as if the material had morphed from rubber into metal.
“It was both astonishing and puzzling,” said Cao, professor in the Department of Physics and corresponding author of the new study. “Our follow-up effort in pursuing a better understanding of the phenomena led us to even more surprising discoveries.”
Now, he and his colleagues think they can explain that astonishing behavior. The group, including several graduate students at CU Boulder, published its most recent results on Oct. 12 in the journal Nature [below].
Drawing on experiments in Cao’s lab, the group reports that, under certain conditions, the honeycomb is abuzz with tiny, internal currents known as chiral orbital currents, or loop currents. Electrons zip around in loops within each of the octahedra in this quantum material. Since the 1990s, physicists have theorized that loop currents could exist in a handful of known materials, such as high-temperature superconductors, but they have yet to directly observe them.
Cao said they could be capable of driving startling transformations in quantum materials like the one he and his team stumbled on.
“We’ve discovered a new quantum state of matter,” Cao said. “Its quantum transition is almost like ice melting into water.”
Colossal changes
The study homes in on a strange property in physics called colossal magnetoresistance (CMR).
In the 1950s, physicists realized that if they exposed certain types of materials to magnets that generate a magnetic polarization, they could make those materials undergo a shift—causing them to switch from insulators to more wire-like conductors. Today, this technology shows up in computer disk drives and many other electronic devices where it helps to control and shuttle electric currents along distinct paths.
The honeycomb in question, however, is vastly different from those materials—the CMR occurs only when conditions avoid that same kind of magnetic polarization. The shift in electrical properties is also much more extreme than what you can see in any other known CMR material, Cao added.
“You have to violate all the conventional conditions to achieve this change,” Cao said.
Melting ice
He and his colleagues, including CU Boulder graduate students Yu Zhang, Yifei Ni and Hengdi Zhao, wanted to find out why.
They, along with co-author Itamar Kimchi of Georgia Institute of Technology, hit on the idea of loop currents. According to the team’s theory, countless electrons circulate around inside their honeycombs at all times, tracing the edges of each octahedron. In the absence of a magnetic field, those loop currents tend to stay disorderly, or flow in both clockwise and counterclockwise patterns. It’s a bit like cars driving through a roundabout in both directions at once.
That disorder can cause “traffic jams” for electrons traveling in the material, Cao said, increasing the resistance and making the honeycomb an insulator.
As Cao put it: “Electrons like order.”
The physicist added, however, that if you pass an electric current into the quantum material in the presence of a specific kind of magnetic field, the loop currents will begin to circulate only in one direction. Put differently, the traffic jams disappear. Once that happens, electrons can speed through the quantum material, almost as if it was a metal wire.
“The internal loop currents circulating along the edges of the octahedra are extraordinarily susceptible to external currents,” Cao said. “When an external electric current exceeds a critical threshold, it disrupts and eventually ‘melts’ the loop currents, leading to a different electronic state.”
He noted that in most materials, the switch from one electronic state to another happens almost instantaneously, or in the span of trillionths of a second. But in his honeycomb, that transformation can take seconds or even longer to occur.
Cao suspects the entire structure of the honeycomb begins to morph, with the bonds between atoms breaking and reforming in new patterns. That kind of reordering takes an unusually long time, he noted—a bit like what happens when ice melts into water.
Cao said the work provides a new paradigm for quantum technologies. For now, you probably won’t see this honeycomb in any new electronic devices. That’s because the switching behavior only takes place at cold temperatures. He and his colleagues, however, are searching for similar materials that will do the same thing under much more hospitable conditions.
“If we want to use this in future devices, we need to have materials that show the same type of behavior at room temperature,” Cao said.
Now, that sort of invention could be buzz-worthy.
Science paper:
Nature
See the full article here .
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As the flagship university of the state of Colorado The University of Colorado-Boulder , founded in 1876, five months before Colorado became a state. It is a dynamic community of scholars and learners situated on one of the most spectacular college campuses in the country, and is classified as an R1 University, meaning that it engages in a very high level of research activity. As one of 34 U.S. public institutions belonging to the prestigious Association of American Universities ), a selective group of major research universities in North America, – and the only member in the Rocky Mountain region – we have a proud tradition of academic excellence, with five Nobel laureates and more than 50 members of prestigious academic academies.
University of Colorado-Boulder has blossomed in size and quality since we opened our doors in 1877 – attracting superb faculty, staff, and students and building strong programs in the sciences, engineering, business, law, arts, humanities, education, music, and many other disciplines.
Today, with our sights set on becoming the standard for the great comprehensive public research universities of the new century, we strive to serve the people of Colorado and to engage with the world through excellence in our teaching, research, creative work, and service.
In 2015, the university comprised nine colleges and schools and offered over 150 academic programs and enrolled almost 17,000 students. Five Nobel Laureates, nine MacArthur Fellows, and 20 astronauts have been affiliated with CU Boulder as students; researchers; or faculty members in its history. In 2010, the university received nearly $454 million in sponsored research to fund programs like the Laboratory for Atmospheric and Space Physics and JILA. CU Boulder has been called a Public Ivy, a group of publicly funded universities considered as providing a quality of education comparable to those of the Ivy League.
The Colorado Buffaloes compete in 17 varsity sports and are members of the NCAA Division I Pac-12 Conference. The Buffaloes have won 28 national championships: 20 in skiing, seven total in men’s and women’s cross country, and one in football. The university has produced a total of ten Olympic medalists. Approximately 900 students participate in 34 intercollegiate club sports annually as well.
On March 14, 1876, the Colorado territorial legislature passed an amendment to the state constitution that provided money for the establishment of the University of Colorado in Boulder, the Colorado School of Mines in Golden, and the Colorado State University – College of Agricultural Sciences in Fort Collins.
Two cities competed for the site of the University of Colorado: Boulder and Cañon City. The consolation prize for the losing city was to be home of the new Colorado State Prison. Cañon City was at a disadvantage as it was already the home of the Colorado Territorial Prison. (There are now six prisons in the Cañon City area.)
The cornerstone of the building that became Old Main was laid on September 20, 1875. The doors of the university opened on September 5, 1877. At the time, there were few high schools in the state that could adequately prepare students for university work, so in addition to the University, a preparatory school was formed on campus. In the fall of 1877, the student body consisted of 15 students in the college proper and 50 students in the preparatory school. There were 38 men and 27 women, and their ages ranged from 12–23 years.
During World War II, Colorado was one of 131 colleges and universities nationally that took part in the V-12 Navy College Training Program which offered students a path to a navy commission.
University of Colorado-Boulder hired its first female professor, Mary Rippon, in 1878. It hired its first African-American professor, Charles H. Nilon, in 1956, and its first African-American librarian, Mildred Nilon, in 1962. Its first African American female graduate, Lucile Berkeley Buchanan, received her degree in 1918.
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University of Colorado-Boulder’s research mission is supported by eleven research institutes within the university. Each research institute supports faculty from multiple academic departments, allowing institutes to conduct truly multidisciplinary research.
The Institute for Behavioral Genetics (IBG) is a research institute within the Graduate School dedicated to conducting and facilitating research on the genetic and environmental bases of individual differences in behavior. After its founding in 1967 IBG led the resurging interest in genetic influences on behavior. IBG was the first post-World War II research institute dedicated to research in behavioral genetics. IBG remains one of the top research facilities for research in behavioral genetics, including human behavioral genetics, psychiatric genetics, quantitative genetics, statistical genetics, and animal behavioral genetics.
The Institute of Cognitive Science (ICS) at CU Boulder promotes interdisciplinary research and training in cognitive science. ICS is highly interdisciplinary; its research focuses on education, language processing, emotion, and higher level cognition using experimental methods. It is home to a state-of-the-art fMRI system used to collect neuroimaging data.
ATLAS Institute is a center for interdisciplinary research and academic study, where engineering, computer science and robotics are blended with design-oriented topics. Part of CU Boulder’s College of Engineering and Applied Science, the institute offers academic programs at the undergraduate, master’s and doctoral levels, and administers research labs, hacker and makerspaces, and a black box experimental performance studio. At the beginning of the 2018–2019 academic year, approximately 1,200 students were enrolled in ATLAS academic programs and the institute sponsored six research labs.[64]
In addition to IBG, ICS and ATLAS, the university’s other institutes include Biofrontiers Institute, Cooperative Institute for Research in Environmental Sciences, Institute of Arctic & Alpine Research (INSTAAR), Institute of Behavioral Science (IBS), JILA, Laboratory for Atmospheric & Space Physics (LASP), Renewable & Sustainable Energy Institute (RASEI), and the University of Colorado Museum of Natural History.
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