For the first time, physicists have witnessed something incredibly exciting: electrons form eddies 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.
“In theory, electron vortices are expected, but there has been no direct evidence, and to see is to believe,” says one of the researchers behind the new study, physicist Leonid Levitov of 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.”
While electrons flowing in a vortex may not seem as innovative, this is a big problem because flowing like a fluid causes more energy to be delivered to the endpoint, rather than getting lost along the way as the electrons get tangled. things like vortex impurities. material or vibrations in atoms.
“We know when electrons enter a fluid state, [energy] low dissipation, and this is interesting to try to design low-power electronics, “says Levitov.” This new observation is a further step in this direction. “
The work was a joint experiment between MIT, the Weizmann Institute of Science in Israel, and the University of Colorado in Denver.
Of course, we already know that electrons can bounce off each other and flow without resistance to superconductors, but this is the result of the formation of something known as “Cooper pairs”, and is not a real example of electrons that they flow collectively like a fluid.
Take water, for example. Water molecules are individual particles, but they travel as one according to the principles of fluid dynamics, transporting each other across a surface, making currents and eddies as they advance.
An electric current should essentially be able to do the same, but any collective behavior of electrons is usually nullified by impurities and vibrations in normal and even semiconductor metals. These “distractions” spin electrons as they travel and prevent them from showing fluid-like behavior.
It has long been predicted that within special materials at temperatures close to zero, these interferences should disappear allowing electrons to move like a fluid … but the problem was that no one had been able to prove that this was the case, until now.
There are two fundamental characteristics of a fluid: linear flow, where the separated particles all flow in parallel as one; and the formation of vortices and eddies.
The first was observed by Levitov and his colleagues at the University of Manchester in 2017 with graphene. In thin sheets of carbon like an atom, 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 function. “The most striking and ubiquitous feature of regular fluid flow, the formation of vortices and turbulence, has not yet been observed in electronic fluids despite numerous theoretical predictions,” the researchers write.
To find out, the team took pure, simple crystals from an ultra-clean material known as tungsten dithelide (WTe2) and cut fine flakes of a single atom.
They then recorded a pattern in a central channel with a circular chamber on either side, creating a “maze” through which an electric current passes. They engraved the same pattern on gold flakes, which do not have the same ultra-clean properties as tungsten ditelide, and therefore acted as a control.
(Aharon-Steinberg et al., Nature, 2022)
Above: The diagram on the left shows how electrons flowed in the experiment on gold flakes (Au). The image on the right shows a simulation of how fluid-like electrons would be expected to behave.
After cooling the material to about -269 degrees Celsius (4.5 Kelvin or -451.57 Fahrenheit) they passed an electric current through it and measured the flow at specific points in the material, to map how the material flowed. electrons.
In the gold flakes, electrons flowed through the maze without changing direction, even when the current had passed through each side chamber before returning to the main current.
Instead, inside the tungsten ditelluride, electrons flowed through the channel and then rotated in each side chamber creating eddies, before returning to the main channel, as expected to make a fluid.
“We observed a change in the direction of flow in the chambers, where the direction of flow reversed direction compared to that of the central strip,” Levitov says.
“This is a very surprising thing, and it’s the same physics as normal fluids, but that happens with electrons at the nanoscale. This is a clear signature that electrons are in a fluid-like regime.”
(Aharon-Steinberg et al., Nature, 2022)
Above: The left column shows how electrons flowed through the tungsten ditellide (WTe2) compared to the hydrodynamic simulations in the left column.
Of course, this experiment was done at very cold temperatures with a specialized material; it’s not something that will happen soon on your home appliances. There were also size limitations in the chambers and the middle channel.
But this is the “first direct visualization of vortex vortices in an electric current,” as the press release explains. This confirmation is not only that electrons can behave like a fluid, but that advancement could also help engineers better understand how to harness this potential in their devices.
The research has been published in Nature.