When an ordinary electrical conductor—such as a metal wire—is connected to a battery, the electrons in the conductor are accelerated by the electric field created by the battery. While moving, electrons frequently collide with impurity atoms or vacancies in the crystal lattice of the wire, and convert part of their motional energy into lattice vibrations. The energy lost in this process is converted into heat that can be felt, for example, by touching an incandescent light bulb.

While collisions with lattice impurities happen frequently, collisions between electrons are much rarer. The situation changes, however, when graphene, a single layer of carbon atoms arranged in a honeycomb lattice, is used instead of a common iron or copper wire.

In graphene, impurity collisions are rare and collisions between electrons play the leading role. In this case, the electrons behave more like a viscous liquid. Therefore, well-known flow phenomena such as vortices should occur in the graphene layer.

Reporting in the journal Science, researchers at ETH Zurich in the group of Christian Degen have now managed to directly detect electron vortices in graphene for the first time, using a high-resolution magnetic field sensor.

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