Scientists have discovered an unusual state of matter in which huge numbers of electrons appear to move slowly together while maintaining their quantum behavior.
The finding, made in an extremely thin magnetic material, could eventually help researchers develop new types of computer memory.
Researchers at the University of Chicago Pritzker School of Molecular Engineering made the discovery while studying a material called Fe5GeTe2.
Their findings, published in Science Advances, challenge existing theories about how the material behaves.
Fe5GeTe2 belongs to a family known as van der Waals magnets. These materials are made from extremely thin layers held together by relatively weak forces, making it possible to separate them into sheets only a few atoms—or potentially a single atomic layer—thick.
Such materials have attracted considerable attention because unusual quantum effects can emerge at these tiny scales. Scientists hope these properties could eventually be used in faster, smaller and more energy-efficient electronic devices.
The research team, led by Assistant Professor Shuolong Yang, used a technique called angle-resolved photoemission spectroscopy, or ARPES, to examine how electrons behave inside Fe5GeTe2.
The technique shines light onto a material and measures electrons that are knocked out of its surface. From this information, researchers can reconstruct the electronic structure of the material and learn how its electrons behave.
When the researchers focused an ultraviolet laser onto a tiny area about 10 micrometers wide, they noticed something unexpected: The material contained what physicists call a “flat band.”
Normally, an electronic band can be imagined somewhat like a sloping landscape. Electrons move more easily along a steeply changing band, much like water rushing down a steep waterfall. When the band is unusually flat, however, the electrons effectively become much slower.
But these electrons were not simply acting independently.
The researchers found evidence that enormous numbers of electrons were interacting and moving collectively while remaining quantum coherent. This is known as a quantum many-body phenomenon, in which the behavior of the whole group cannot be understood simply by looking at individual particles.
The finding was particularly surprising because existing theories did not predict this behavior in Fe5GeTe2. According to the researchers, scientists may now need to reconsider their understanding of the magnetic interactions inside the material.
The unexpected behavior could also have technological value.
Fe5GeTe2 can exist in different magnetic and electronic states. If those states can be reliably controlled, they could potentially represent different pieces of information, similar to the zeros and ones used in conventional computer memory.
The researchers are already experimenting with a tightly focused laser to switch the material between the newly discovered quantum state and other states. If such switching can be precisely controlled, it could provide the foundation for a new kind of memory device.
One major challenge remains temperature. Many unusual quantum effects disappear unless materials are kept extremely cold. Encouragingly, the newly observed behavior remained coherent at temperatures up to around 100 degrees above absolute zero, although that is still far below room temperature.
The team now wants to determine whether the effect can eventually work at room temperature and whether it survives when Fe5GeTe2 is reduced to a single atomic layer.
If successful, these strange slow-moving electrons could help turn an unexpected quantum discovery into a new way of storing digital information.
