At the University of Chicago, physicists probing a layered magnetic material called Fe5GeTe2 encountered something the prevailing theory did not anticipate: millions of electrons moving in collective slow-motion while remaining quantum coherent, a phenomenon known as a flat electronic band. The discovery, emerging from a technique that uses photons to illuminate the hidden energy lives of electrons, challenges the field's existing models of how magnetism and quantum behavior interact in this class of materials. It is a reminder that nature's deepest structures often refuse to conform to our mo
Scientists discover electrons moving in quantum slow-motion in magnetic material
Millions of electrons moving together in quantum slow-motion
Mark
So electrons are moving slowly in this material—but what makes that a discovery? Doesn't everything move slowly at some temperature?
Mimi
The key is that they're moving slowly while staying quantum coherent. Normally, when electrons slow down, they lose that quantum behavior. Here, millions of them are moving together in lockstep, which shouldn't happen according to the theory.
Luke
How do we know they're actually coherent? ARPES shows you the energy states, but coherence is a specific claim.
Mimi
That's fair. The flat band itself is the signature—it's what you see when electrons are in a collective quantum state. The coherence is inferred from that structure.
Mark
And this matters for memory because...?
Mimi
The material can exist in different magnetic states. If you can switch between them with a laser, you could use those states to store information—like 0 and 1 in a computer.
Luke
But they haven't actually built a memory device yet. They've shown the switching might be possible, not that it works.
Mimi
Right. They're still in the exploratory phase. The real test is whether this survives in a single atomic layer and at higher temperatures.
Mark
How much higher would it need to go?
Mimi
Room temperature. Right now it works up to 100 Kelvin, which is about minus 173 Celsius. That's progress, but still a long way off.
Luke
And we don't know if the effect even persists in the thin-layer form yet?
Mimi
No. That's the next experiment. If it doesn't, the whole practical application falls apart.
Mark
So this is really a theoretical puzzle that might become useful someday?
Mimi
Exactly. The immediate value is understanding why the material behaves differently than predicted. The practical value is still speculative.
Le Pouls
- Theory predicted one thing; the material did another—millions of electrons in Fe5GeTe2 were caught moving in coordinated quantum slow-motion, a flat-band phenomenon no existing model had forecast for this material.
- The contradiction is not a minor correction but a foundational one: the team must now reconsider the magnetic interactions inside Fe5GeTe2 from the ground up, reopening questions physicists believed were settled.
- The coherent quantum behavior persists up to 100 Kelvin—far colder than a kitchen, but unusually warm for this class of effect, nudging the phenomenon meaningfully closer to practical relevance.
- Researchers are now testing whether a focused laser can flip the material between quantum phases, an early but promising step toward a memory device that stores information in distinct magnetic states.
- The final hurdle—whether these properties survive when the material is peeled to a single atomic layer—will determine if the discovery can cross from laboratory curiosity into functional technology.
At the University of Chicago, physicists probing a layered magnetic material called Fe5GeTe2 encountered something the prevailing theory did not anticipate: millions of electrons moving in collective slow-motion while remaining quantum coherent, a phenomenon known as a flat electronic band. The discovery, emerging from a technique that uses photons to illuminate the hidden energy lives of electrons, challenges the field's existing models of how magnetism and quantum behavior interact in this class of materials. It is a reminder that nature's deepest structures often refuse to conform to our most careful predictions—and that such refusals sometimes point toward new possibilities, in this case the prospect of memory technologies built on quantum rather than classical principles.
A team at the University of Chicago has uncovered an unexpected quantum phenomenon inside Fe5GeTe2, a layered magnetic material belonging to the van der Waals family first synthesized seven years ago. Using angle-resolved photoemission spectroscopy—a technique that fires photons at a surface to reveal how electrons behave—Assistant Professor Shuolong Yang and colleagues including postdoctoral researchers Gabriele Berruto and Qiang Gao observed something their theoretical models did not predict.
When an ultraviolet laser was focused onto a region just ten micrometers across, the material displayed a flat electronic band. Where ordinary materials offer electrons a range of energies and speeds, a flat band collapses that range entirely. The electrons slow to a crawl—not individually, but as a vast, synchronized collective, maintaining quantum coherence across thousands or millions of particles at once. Yang likens it to water on a nearly level slope: the shallower the incline, the slower the flow. The finding suggests the magnetic interactions inside Fe5GeTe2 are fundamentally different from what current theory describes, requiring the field to revisit the material's underlying physics.
The discovery carries practical weight as well. Because Fe5GeTe2 can exist in multiple distinct magnetic states, those states could in principle encode information—the essential requirement of a memory device. Early experiments suggest a focused laser may be able to switch the material between its quantum many-body phase and other phases, a capability that could eventually be engineered into a working device. The coherent behavior was observed up to 100 Kelvin, which remains far below room temperature but is notably warm for a quantum effect of this kind, making it more viable than many comparable phenomena.
The team's next steps involve determining whether these properties survive when the material is thinned to a single atomic layer—a critical test for real-world integration. The paper also carries a quiet tribute: it stands among the final publications of Peter Littlewood, a distinguished theoretical physicist at the university who died on June 15, and to whom Yang dedicated the work.
A team at the University of Chicago has found something unexpected in a layered magnetic material called Fe5GeTe2: millions of electrons moving together in a state of quantum slow-motion, all while maintaining the coherence that quantum mechanics demands. The discovery, published in Science Advances, upends what physicists thought they understood about how this material behaves at the atomic level.
Fe5GeTe2 belongs to a family of materials known as van der Waals magnets, first synthesized seven years ago. These materials can be peeled into atomically thin layers, which is why researchers have been investigating them as potential building blocks for memory technologies that work differently from conventional magnetic storage. Assistant Professor Shuolong Yang's lab at the University of Chicago Pritzker School of Molecular Engineering set out to map the electronic structure of Fe5GeTe2 using angle-resolved photoemission spectroscopy, a technique that fires photons at a material's surface to knock electrons loose and reveal their energy states and behavior.
What Yang and his colleagues—including postdoctoral researchers Gabriele Berruto and Qiang Gao—observed was not what theory predicted. When they focused an ultraviolet laser onto a region just ten micrometers across, the material displayed what physicists call a flat electronic band. In ordinary materials, electrons have a range of energies available to them as they conduct electricity. In a flat band, that range collapses. The electrons do not move through the material at their normal speed. Instead, they slow down dramatically while behaving as a collective unit—thousands or millions of them moving together in a coordinated, quantum-coherent way. Yang describes it as a quantum many-body phenomenon, something genuinely strange: not the measurement of individual electrons, but the synchronized motion of vast numbers of them.
The analogy Yang offers is water on a slope. A steep incline sends water rushing downward; a shallow one produces a slow trickle. The flat electronic band works similarly—it is the quantum equivalent of a shallow slope, causing electrons to move at a crawl. This behavior contradicts what existing theory says should happen in Fe5GeTe2's magnetic structure. Berruto noted that from a scientific standpoint, the discovery suggests the magnetic interactions within the material are fundamentally different from what the models predict. The team will need to reconsider the material's underlying physics from the ground up.
Beyond the theoretical puzzle, the finding opens a practical door. Because Fe5GeTe2 can exist in multiple distinct magnetic states, those states could potentially encode and store information—the basic requirement for a memory device. Yang's group is now testing whether a tightly focused laser can switch the material between this quantum many-body phase and other phases. Early results suggest such switching is possible, which could eventually lead to incorporating this effect into a working memory device.
One significant advantage emerged from the measurements: the coherent behavior persisted up to 100 degrees above absolute zero. That is still far colder than room temperature, but it is relatively warm compared with other quantum materials exhibiting similar effects, making it more promising for eventual real-world use. Gao, now a research scientist at Lawrence Berkeley National Laboratory, noted that any practical memory device would need to operate at room temperature—a threshold the team has not yet reached but has moved closer to. The next phase of investigation will determine whether these same properties survive when Fe5GeTe2 is exfoliated down to a single atomic layer, a critical test for whether the material could actually be integrated into a functional device.
The paper represents one of the final publications from Peter Littlewood, a distinguished theoretical physicist at the University of Chicago who died on June 15. Yang dedicated the work to him, acknowledging Littlewood's role as a leader in quantum materials research at the institution.
Citations marquantes
We're measuring the interaction of thousands or millions of electrons, and they are all moving together in a coherent way. That's a quantum many-body phenomenon, and it's actually a very weird thing.— Assistant Professor Shuolong Yang, University of Chicago
From a scientific perspective, this suggests that the magnetic interactions within the material are totally different from what theory predicts.— Gabriele Berruto, postdoctoral researcher
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