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Swirling electrons detected in graphene

Using a highly sensitive quantum sensor, researchers have directly observed electron vortices forming in micrometer-sized graphene disks, shedding light on the unique fluid-like behavior of electrons in this wonder material.

Swirling electrons detected in graphene

Using a magnetic field sensor (red arrow) inside a diamond needle, researchers at ETH imaged electron vortices in a graphene layer (blue). (Illustration courtesy: Chaoxin Ding)

Electrons, the fundamental particles carrying electrical charge, typically flow through conductors like marbles rolling down a bumpy hill, frequently colliding with impurities. This results in energy loss, often observed as heat. However, in the pristine landscape of graphene, a single layer of carbon atoms arranged in a honeycomb lattice, electrons encounter fewer obstacles. This allows them to interact more freely, behaving not as individual particles, but as a collective, akin to a viscous fluid.

This fluid-like behavior, predicted by theoretical physicists, suggests that electrons in graphene should exhibit fascinating flow patterns, including the formation of swirling vortices. Now, researchers at ETH Zurich, led by Christian Degen, have directly observed these electron vortices for the first time.

Their breakthrough utilizes a highly sensitive magnetic field sensor based on a nitrogen-vacancy (NV) center in a diamond. This quantum sensor, positioned nanometers above the graphene surface, detects the minute magnetic fields generated by the swirling motion of electrons.

The team fabricated micrometer-sized graphene disks connected to a conducting strip. As predicted, electron vortices emerged within the smaller disks, evidenced by a characteristic reversal in the flow direction compared to the surrounding strip. Larger disks, however, did not exhibit this vortex formation, aligning with theoretical expectations.

“Thanks to our extremely sensitive sensor and high spatial resolution, we didn’t even need to cool down the graphene and were able to conduct the experiments at room temperature”, explains Marius Palm, a former PhD student on the project.

Beyond electron vortices, the team also observed similar swirling patterns formed by “holes,” the absence of electrons that can also carry charge. Interestingly, at the charge neutrality point, where electrons and holes exist in a delicate balance, the vortices vanish entirely.

This research provides a crucial glimpse into the fascinating world of electron hydrodynamics in graphene. While fundamental in nature, these findings lay the groundwork for exploring exotic electron transport phenomena in other materials and designing novel electronic devices that exploit the fluid-like behavior of electrons.

The original article can be accessed at Science magazine.

The original story can be accessed here.

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Dr. Ravindra Shinde is the editor-in-chief and the founder of The Science Dev. He is also a research scientist at the University of Twente, the Netherlands. His research interests include computational physics, computational materials, quantum chemistry, and exascale computing. His mission is to disseminate cutting-edge research to the world through succinct and engaging cover stories.

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