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After years of research, physicists observe the flow of electrons in fluid vortices

For the first time, physicists witnessed something incredibly exciting: electrons swirling like a fluid.

This behavior is one that scientists have long predicted, but never observed before. And it could be the key to developing more efficient and faster next-generation electronics.

“Electron vortices are expected in theory, but there has been no direct evidence, and seeing is believing,” says one of the researchers behind the new study, physicist Leonid Levitov. from MIT.

“Now we’ve seen it, and it’s a clear signature of being in this new regime, where electrons behave like a fluid, not like individual particles.”

Although electrons flowing in a vortex might not seem so groundbreaking, it’s a big deal because flowing like a fluid results in more energy being delivered to the endpoint, instead of being lost along the way. while electrons are jostled about by such things as impurities in matter or vibrations in atoms.

“We know when electrons enter a fluid state, [energy] the dissipation drops, and that’s interesting when trying to design low-power electronics,” says Levitov. “This new observation is another step in that direction.

The work was a joint experiment between MIT, the Weizmann Institute for Science in Israel and the University of Colorado at Denver.

Of course, we already know that electrons can bounce off each other and flow without resistance in superconductors, but this is the result of the formation of something known as “Cooper pairs”, and this is not This is not a true example of electrons flowing collectively as a fluid.

Take water, for example. Water molecules are individual particles, but they travel as one according to the principles of fluid dynamics, transporting themselves across a surface, creating streams and eddies as they go.

An electric current should essentially be able to do the same thing, but any collective behavior of electrons is usually negated by the impurities and vibrations of normal metals and even semiconductors. These “distractions” knock the electrons upside down as they move and prevent them from exhibiting fluid-like behavior.

It has long been predicted that in special materials at near-zero temperatures, these interferences should disappear, allowing electrons to move like a fluid…but the problem was that no one had been able to prove that. was the case, until now.

There are two basic characteristics of a fluid: linear flow, where separate particles all flow in parallel as one; and the formation of eddies and eddies.

The first was observed by Levitov and his colleagues at the University of Manchester in 2017 using graphene. In atom-thin sheets of carbon, Levitov and his team showed that an electric current could flow through a pinch point like a fluid, rather than like grains of sand.

But no one had seen the second feature film. “The most striking and pervasive feature in smooth fluid flow, the formation of vortices and turbulence, has not yet been observed in electronic fluids despite numerous theoretical predictions,” the researchers write.

To figure this out, the team took pure single crystals of an ultra-clean material known as tungsten ditelluride (WTe2) and cut into single-atom thin flakes.

They then etched a pattern into a central channel with a circular chamber on each side, creating a “labyrinth” for the passage of an electric current. They etched the same pattern on gold flakes, which do not have the same ultra-clean properties as tungsten ditelluride and therefore served as a control.

GoldExperienceversusFluid(Aharon-Steinberg et al., Nature2022)

Above: The diagram on the left shows how electrons flowed in the experiment in flakes of gold (Au). The image on the right shows a simulation of how they would expect fluid electrons to behave.

After cooling the material to around -269 degrees Celsius (4.5 Kelvin or -451.57 Fahrenheit), they passed an electric current through it and measured the flux at specific points throughout the material, to map the circulation electrons.

In the gold flakes, the electrons passed through the labyrinth without changing direction, even when the current had passed through each side chamber before returning to the main current.

In contrast, in tungsten ditelluride, electrons passed through the channel, then swirled through each side chamber, creating vortices, before flowing back into the main channel, as one would expect a fluid to do.

“We observed a change in the direction of the flow in the chambers, where the direction of the flow reversed the direction compared to that of the central strip,” explains Levitov.

“It’s a very striking thing, and it’s the same physics as ordinary fluids, but it happens with nanoscale electrons. It’s a clear signature of electrons being in a regime like fluid.”

SimulationsVersusElectron Flow(Aharon-Steinberg et al., Nature2022)

Above: Left column shows how electrons passed through tungsten ditelluride (WTe2) compared to left-hand hydrodynamic simulations column.

Of course, this experiment was carried out in ultra-cold temperatures with specialized material – it’s not something that will be happening in your home gadgets anytime soon. There were also size constraints on the chambers and the middle channel.

But this is the “first direct visualization of swirling vortices in an electric current” as the press release explains. Not only this confirmation that the electrons box to behave like a fluid, this breakthrough could also help engineers better understand how to exploit this potential in their devices.

The research has been published in Nature.

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