Physicists at the University of Chicago's Pritzker School of Molecular Engineering have identified an unexpected electronic behaviour in a two-dimensional magnetic material, one that could point the way to a new class of computer memory.
The material, Fe5GeTe2, belongs to a family known as van der Waals magnets: crystals built from atomically thin layers held together by weak forces, which allows them to be peeled apart or stacked much like sheets of paper. Discovered seven years ago, Fe5GeTe2 has drawn attention because its layered structure could enable new kinds of memory technologies with advantages over those built from conventional magnetic materials.
Electrons that move together, and slowly
Using a technique called angle-resolved photoemission spectroscopy, or ARPES, which fires photons at a material to knock electrons loose and measure their energy and momentum, the team led by assistant professor Shuolong Yang studied how electrons behave inside Fe5GeTe2. Working with postdoctoral researchers Gabriele Berruto and Qiang Gao, Yang's group found that the material enters what is known as a charge-ordered state, in which large groups of electrons move collectively at exceptionally low effective speeds while still behaving as a single coherent quantum system.
In most materials, an electron's energy band, essentially a map of how its energy changes as it moves, slopes steeply when electrons travel easily through the crystal. A flat band, by contrast, signals that motion is being suppressed, in this case by interactions between the electrons themselves rather than by any external constraint. The team's results, published in the journal Science Advances, describe this as an interaction-driven flat band, a phenomenon that has been theorised in other systems but not previously confirmed in this material.
“"This is a fundamental discovery that deviates from theoretical predictions," said Shuolong Yang. "We now have to go back and think about the magnetic interactions of this material from scratch, but it also leads to new possibilities in using this material for new kinds of memory devices."”
Why it matters for memory chips
The behaviour persists up to roughly 100 Kelvin, or about minus 173 degrees Celsius, still far colder than room temperature but within reach of specialised cooling systems already used in some quantum computing hardware. Because the charge-ordered state can potentially be switched using light, researchers see a route towards memory devices that combine conventional magnetic data storage with the added stability of quantum coherent states, according to coverage of the findings reported by the science news outlet Bioengineer.org.
Van der Waals magnets have been studied intensively since the discovery of two-dimensional magnetism in materials such as Cr2Ge2Te6 and CrI3 nearly a decade ago, work that opened the door to ultrathin spintronic devices. For European research institutions and semiconductor firms watching the race to miniaturise memory and quantum hardware, from imec in Belgium to CEA-Leti in France, findings like this one are closely tracked, since atomically thin materials are seen as a potential path beyond the physical limits of silicon-based chips.
The Chicago team's next step, as with much quantum materials research, will be determining whether the slow-electron state can be controlled reliably enough, and at a high enough temperature, to be useful outside the laboratory. That remains an open question, but the discovery itself adds a genuinely new entry to the physics of layered magnetic materials.
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