Once that happens, electrons can speed through the quantum material, almost as if it was a metal wire. Put differently, the traffic jams disappear. 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. That disorder can cause “traffic jams” for electrons traveling in the material, Cao said, increasing the resistance and making the honeycomb an insulator. It’s a bit like cars driving through a roundabout in both directions at once. In the absence of a magnetic field, those loop currents tend to stay disorderly, or flow in both clockwise and counterclockwise patterns. According to the team’s theory, countless electrons circulate around inside their honeycombs at all times, tracing the edges of each octahedron. They, along with co-author Itamar Kimchi of Georgia Institute of Technology, hit on the idea of loop currents. He and his colleagues, including CU Boulder graduate students Yu Zhang, Yifei Ni and Hengdi Zhao, wanted to find out why. “You have to violate all the conventional conditions to achieve this change,” Cao said. The shift in electrical properties is also much more extreme than what you can see in any other known CMR material, Cao added. The honeycomb in question, however, is vastly different from those materials-the CMR occurs only when conditions avoid that same kind of magnetic polalrization. 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. In the 1950s, physicists realized 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. The study homes in on a strange property in physics called colossal magnetoresistance (CMR). “Its quantum transition is almost like ice melting into water.” “We’ve discovered a new quantum state of matter,” Cao said. Since the 1990s, physicists have theorized such loop currents could exist in a handful of known materials, such as high-temperature superconductors, but they have yet to directly observe them.Ĭao said they could be capable of driving startling transformations in quantum materials like the one he and his team stumbled on. Electrons zip around in loops within each of the octahedra in this quantum material. 12 in the journal Nature.ĭrawing 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. The group, including several graduate students at CU Boulder, published its most recent results online Oct. Now, he and his colleagues think they can explain that astonishing behavior. “Our follow-up effort in pursuing a better understanding of the phenomena led us to even more surprising discoveries.” “It was both astonishing and puzzling,” said Cao, professor in the Department of Physics and corresponding author of the new study. It was almost as if the material had morphed from rubber into metal. When they exposed the honeycomb to magnetic fields in a certain way, however, it suddenly became millions of times less resistant to currents. ![]() In other words, it did not allow electric currents to pass through it easily. 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. 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. ![]() The quantum material in question is known by the chemical formula Mn3Si2Te6. The findings from researchers at CU Boulder may one day help engineers develop new kinds of devices, such as quantum sensors or the quantum equivalent of computer memory storage devices. A series of buzzing, bee-like “loop-currents” could explain a recently discovered, never-before-seen phenomenon in a type of quantum material.
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