Using a magnetic field sensor inside a diamond needle, researchers at ETH imaged electron vortices in a graphene layer . Credit: Chaoxin Ding
Typically, transport phenomena are more easily detected at low temperatures. Thanks to their highly sensitive sensor, the ETH researchers were able to observe vortices even at room temperature. 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.
“Because of the tiny dimensions of the diamond needle and the small distance from the graphene layer – only around 70 nanometers – we were able to make the electron currents visible with a resolution of less than a hundred nanometers,” says Marius Palm, a former PhD student in Degen’s group. This resolution is sufficient for seeing the vortices.In their measurements, the researchers observed a characteristic sign of the expected vortices in the smaller discs: a reversal of the flow direction.
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