Electric Vortex Observed For The First Time

An electric vortex has been witnessed for the first time, admittedly on a much smaller scale than this. Image Credit: Christine Daniloff, MIT

Physicists have observed electric eddies created by electrons interacting in a similar way to water molecules in whirlpools, finally confirming long-standing predictions of theorists.

When teaching electricity, a popular but widely criticized analogy is that of water flowing through a pipe, with voltage being the reciprocal of the change in elevation, and current the amount of flow in a circuit. Some students find the analogy useful, but many physicists find it misleading because of the differences in the way electrons and water molecules behave.

However, in certain materials, the analogy becomes true; The electrons affect each other in a way that is more like interactions between water molecules, leading to liquid-like behavior. One such form of behavior is the creation of whirlpools, which have now been described in Nature for the first time, having previously proved elusive.

“Electron vortexes are expected in theory, but there is no direct evidence yet, and seeing is believing,” said MIT Professor Leonid Levitov in a statement. “Now we’ve seen it, and it’s a clear sign of being in this new regime, where electrons behave as liquids, not as individual particles.”

Among the strange phenomena witnessed under such conditions are negative resistance and “superballistic electron flow” in which electrons appear to work together to pass through narrow gaps.

An individual electron moving as part of an electric current is subject to a variety of forces. This includes the movement of atoms in the conducting material and impurities that may affect its flow, as well as the stresses that cause it to move. Other electrons that are also part of the flow have an influence as well, but in most materials, these are small compared to the rest. Superconducting materials, in which electron pairs move more smoothly than is possible for single electrons, are a partial exception.

However, if you can dampen them all, the quantum interactions between electrons become dominant. The electrons move as a viscous liquid. To achieve this state the materials in which they travel need to be cleaned of impurities and cooled to near absolute zero, so that the atomic motion almost disappears.

Using these properties, Levitov and colleagues achieved a nearly unimpeded flow of electrons through graphene in 2017. However, water doesn’t always flow smoothly. Instead, it can become turbulent, and even create eddies. The authors had not observed comparable behavior in graphene, so they turned to single-atom-thick tungsten ditelluride (WTe) sheets (WTe).₂) instead.

Not only WTe₂ emitting the wave-like properties of electrons, Levitov notes: “The material is very clean, which makes fluid-like behavior directly accessible.” The authors carved a channel running between the two circular spaces onto the WTe2 and gold sheets for comparison. When current flows through the pattern in a 4.5°K (-451°F) magnetic field it reveals the behavior of the electrons.

In tungsten ditelluride, electrons flowing into side channels form whirlpools, but this is not the case in gold. Image Credit: Aharon-Steinberg et al/Alam

The authors were able to watch electrons swirl in and out of the side chamber creating tiny whirlpools on their way, but only in tungsten ditelluride, not gold.

“We observed a change in the direction of flow in space, where the flow direction reversed compared to in the middle lane,” Levitov said. “That’s a very striking thing, and the physics is the same as in ordinary liquids, but happens with electrons at the nanoscale. The electron signatures are clearly in a fluid-like regime. ”

The conditions that need to be carefully controlled to produce these whirlpools – if the gap through which electrons flow widens, votrics, and indeed turbulence – disappears. Close to the transition point where smooth flow replaces turbulence, the eddies are seen splitting in half, one of the behaviors Levitov and the team expected to witness.

It is hoped the observations will have real-world applications such as leading to ways to power low-energy electronics more efficiently.

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