Over the past decade, scientists have made major progress in creating two-dimensional materials with unusual quantum properties that could eventually support a new generation of technologies. Some of these materials can become superconductors, allowing electricity to flow without energy loss, while others develop charge orders, in which electrons settle into organized patterns instead of moving freely. Researchers at the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) have now uncovered an unexpected form of behavior in one such material, Fe5GeTe2.
They found that it can enter a charge-ordered state where large numbers of electrons move together extremely slowly while still maintaining quantum coherence. The findings, published in Science Advances, came from the laboratory of Asst. The discovery challenges existing ideas about how the material behaves and may also point toward new technological uses.
"This is a fundamental discovery that deviates from theoretical predictions," Yang said. "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." Fe5GeTe2, discovered seven years ago, belongs to a family of materials known as van der Waals magnets. Because these materials can be formed into atomically thin layers, researchers are exploring whether they could enable memory technologies that differ from those built with conventional magnetic materials.
Yang and his colleagues, including postdoctoral scholars Gabriele Berruto and Qiang Gao, examined Fe5GeTe2 using angle-resolved photoemission spectroscopy (ARPES). The technique shines photons onto a material and ejects electrons from its surface, allowing researchers to map its electronic structure and magnetic states. The team focused an ultraviolet laser onto an area just 10 micrometers across.
What they saw was unexpected. The material displayed a flat electronic band, meaning that the range of electron energies associated with electrical conduction changed very little. In a flat band, electrons do not move through the material as quickly as they normally would.
Instead, they can become extremely slow while behaving collectively. "We're not measuring one electron," Yang said. "We're measuring the interaction of thousands or millions of electrons, and they are all moving together in a coherent way.
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