Although they are separate molecules, water molecules collectively flow as a liquid, producing currents, waves, vortices, and other classical fluid phenomena.
Not so with electricity. While electric current is also a different construction of particles – in this case, electrons – the particles are so small that any collective behavior between them drowns out the larger effect when electrons pass through ordinary metals. But in some materials and under certain conditions, this effect fades, and electrons can affect each other directly. In this case, the electrons can flow collectively like a liquid.
Now, physicists at the Massachusetts Institute of Technology and the Weizmann Institute of Science have observed electrons flowing in eddies, or eddies – fluid flow characteristics that theorists predicted electrons would exhibit, but so far haven’t seen.
“Electronic eddies are theoretically expected, but there is no direct evidence, and visibility is uncertain,” said Leonid Levitov, a professor of physics at MIT. “We’ve seen it now, and it’s clear evidence of being in this new system, where electrons behave like liquids, not as individual particles.”
The observations, published today in Nature, could help design more efficient electronics.
We know that when electrons move in the liquid state, [energy] Dissipation drops, which is important in trying to design low-power electronics,” Levitov said. “This new observation is another step in that direction.”
Levitov is a co-author of the new research paper, along with Eli Zeldov and others at the Weizmann Institute of Science in Israel and the University of Colorado in Denver.
collective pressure
When electricity passes through most metals and ordinary semiconductors, the path of torque and electrons in the current is affected by impurities in the material and vibrations between the atoms of the material. This process dominates the behavior of electrons in ordinary materials.
But theorists have speculated that in the absence of such an ordinary classical process, quantum effects would take over. That is, the electrons must pick up on the exact quantum behavior of each other and move collectively, like liquid electrons thick like honey. This fluid-like behavior will occur in ultrapure materials and at near-zero temperatures.
In 2017, Levitov and colleagues at the University of Manchester reported signs of fluid-like electron behavior in graphene, an atomic-thick sheet of carbon in which thin channels have been etched at multiple pressure points. They note that the current sent through the line can flow through a resistance of less resistance. This suggests that the electrons in the stream are able to squeeze through pressure points collectively, like a liquid, rather than clogging, like individual grains of sand.
This first indication prompted Levitov to explore other electrofluidic phenomena. In the new study, he and his colleagues at the Weizmann Institute of Science looked at the visualization of electron vortices. As they write in their paper, “The most striking and widespread features of uniform fluid flow, the formation of vortices and turbulence, have not been observed in electron fluids despite some theoretical predictions.”
flow route
To visualize electron vortices, the team looked at tungsten diethyloride (WTe2), a very pure metal compound that has been found to exhibit strange electronic properties when isolated in single, thin, two-dimensional atomic form.
“Tungsten ditelluride is one of the new quantum materials in which electrons interact energetically and behave as quantum waves rather than particles,” Levitov said. “Additionally, the material is very clean, which makes direct access to the fluid-like behavior available.”
The researchers synthesized pure single crystals of tungsten dichloride, and exfoliated thin flakes of the material. They then used electron beam lithography and plasma etching techniques to model each slice in the central channel connected to circular spaces on either side. They engrave the same pattern on thin gold foil – a standard metal with ordinary and classic electronic properties.
They then passed a current through each patterned sample at a very low temperature of 4.5 K (about -450 degrees Fahrenheit) and measured the current flow at specific points in each sample, using a nano-scanning superconducting quantum interference device (SQUID) on the tip. . . The device was developed in Zeldov’s laboratory and measures magnetic fields with very high accuracy. By using a device to scan each sample, the team was able to observe in detail how electrons flow through the patterned channels in each material.
The researchers noted that electrons flowing through the gold foil patterned channels did so without reversing, even as some of the current passed through each side chamber before joining the main current. In turn, the electrons flowing through the tungsten dichloride flow through the channels and spin into each side chamber, just as water does when it is discharged into a vessel. The electrons form tiny eddies in each chamber before flowing back into the main channel.
“We observed a change in the direction of flow in space, where the direction of the flow was reversed compared to in the middle lane,” Levitov said. “This is something really amazing, the same physics found in ordinary liquids, but it happens with electrons at the nanoscale. This is clear evidence that electrons exist in fluid-like systems.”
The group observation is the first direct visualization of vortex vortexes in electric current. The result was an experimental confirmation of the fundamental nature of electron behavior. They can also provide clues on how engineers can design low-power devices that conduct electricity in a more flexible way and with less impedance.
“Viscous electron flow fingerprints have been reported in a number of experiments on different materials,” said Klaus Enslin, professor of physics at ETH Zurich in Switzerland, who was not involved in the study. “The theoretical predictions of eddy-like current flow have now been confirmed experimentally, adding an important milestone in the investigation of this new transmission system.”
This research was supported in part by the European Research Council, the German-Israeli Foundation for Scientific Research and Development, and the Israel Science Foundation.
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