Physicists see electron whirlpools for the first time(news.mit.edu)
news.mit.edu
Physicists see electron whirlpools for the first time
https://news.mit.edu/2022/electron-whirlpools-physics-0706
24 comments
Complete article pdf is available on the arxiv server:
https://arxiv.org/abs/2202.02798
Helpful background article
"Imaging the breakdown of ohmic transport in graphene" (Jenkins et al. 2020)
https://arxiv.org/abs/2002.05065
> "Ohm’s law states that the current flow through an electrical conductor is proportional to a voltage difference across it. While this introductory textbook physics is ubiquitous in macroscopic electrical devices, Ohm’s law need not hold locally at every point inside of a conductor. Specifically, Ohm’s law arises only on length scales sufficiently long that microscopic scattering processes completely relax the electrical current. In an ordinary metal, impurity scattering and umklapp processes, each of which relax current, dominate the electronic dynamics; hence Ohm’s law arises on scales larger than the electronic mean free path... In this regime, electrical transport is diffusive. However, in low-density, low-disorder Fermi liquids, it was predicted decades ago that dynamics could be dominated by electron-electron collisions, which conserve momentum... the momentum-conserving collisions do not completely relax the electrical current, resulting in viscous rather than diffusive transport, with current flow resembling that of a fluid."
This seems to be more of an improved experimental method than anything else. The 'possible practical applications' claim in the article headline is probably there to draw in investments for startups or to justify the next round of grant applications. This is why it's almost always best to ignore the university media office press releases (which are generally one-sided puffery) and just look at the papers themselves, and perhaps independent science articles. The actual important big-picture result seems to be this:
> "More broadly, these techniques provide a powerful method for visualizing electronic dynamics normally invisible in bulk resistivity measurements."
https://arxiv.org/abs/2202.02798
Helpful background article
"Imaging the breakdown of ohmic transport in graphene" (Jenkins et al. 2020)
https://arxiv.org/abs/2002.05065
> "Ohm’s law states that the current flow through an electrical conductor is proportional to a voltage difference across it. While this introductory textbook physics is ubiquitous in macroscopic electrical devices, Ohm’s law need not hold locally at every point inside of a conductor. Specifically, Ohm’s law arises only on length scales sufficiently long that microscopic scattering processes completely relax the electrical current. In an ordinary metal, impurity scattering and umklapp processes, each of which relax current, dominate the electronic dynamics; hence Ohm’s law arises on scales larger than the electronic mean free path... In this regime, electrical transport is diffusive. However, in low-density, low-disorder Fermi liquids, it was predicted decades ago that dynamics could be dominated by electron-electron collisions, which conserve momentum... the momentum-conserving collisions do not completely relax the electrical current, resulting in viscous rather than diffusive transport, with current flow resembling that of a fluid."
This seems to be more of an improved experimental method than anything else. The 'possible practical applications' claim in the article headline is probably there to draw in investments for startups or to justify the next round of grant applications. This is why it's almost always best to ignore the university media office press releases (which are generally one-sided puffery) and just look at the papers themselves, and perhaps independent science articles. The actual important big-picture result seems to be this:
> "More broadly, these techniques provide a powerful method for visualizing electronic dynamics normally invisible in bulk resistivity measurements."
It says that this could help with semiconductor design but I'm curious how. From what I can tell we only observe this behavior in very specific materials at incredibly low temperatures.
Is it as simple as "understanding electricity better will let us design electronics better?"
Apologies if this is a silly question, I'm completely out of my depth.
Is it as simple as "understanding electricity better will let us design electronics better?"
Apologies if this is a silly question, I'm completely out of my depth.
I would imagine for the low temperature environment of space and satellites, but it might also improve the lifetime of circuit boards during powerup cycles. Its reported that power cycling stresses the circuit boards more than just leaving them switched on, so I wouldnt be surprised to see some changes made in everyday electronic devices. With that in mind, will we see less 90 degree turns on circuit boards in order to ensure the smooth flow of electrons, even though we cant yet detect any Oxbow (Resacas) "lakes" in circuit boards due to the rather rigid nature of circuit board design & materials.
I would also imagine this "electron fluid" only applies to DC circuit applications, because AC electrons are perhaps best represented by every discerning business executive's desktop toy known as Newtons Cradle.
I would also imagine this "electron fluid" only applies to DC circuit applications, because AC electrons are perhaps best represented by every discerning business executive's desktop toy known as Newtons Cradle.
90 degree turns don't "wear out" as such, it's usually more that they (might) produce a reflection in a high-speed line. This is why high-speed traces are often curved. Also 90-degree corners can concentrate mechanical stress and act as acid traps which affect manufacturability. They're also ugly (and I'm only half joking).
Power-up failure of a PCB is far more likely to be due to inrush current burning something out or thermal cycling leading to a broken connection than a viscous-current effect.
Also, space-based devices aren't always cold: it actually takes a lot of engineering to keep them from overheating unless they're in perpetual shade, and even then you need to do more work to get to a superconductive regime.
Power-up failure of a PCB is far more likely to be due to inrush current burning something out or thermal cycling leading to a broken connection than a viscous-current effect.
Also, space-based devices aren't always cold: it actually takes a lot of engineering to keep them from overheating unless they're in perpetual shade, and even then you need to do more work to get to a superconductive regime.
I'm also not seeing any immediate connection to better electronics. Maybe the resulting phenomena will be exploited to make better instruments that can be used in labs with cryo capability.
Maybe the effects will be replicated in other materials or higher temperatures someday, and the experience won here will be important.
Regardless, it's cool to know it's been witnessed.
Maybe the effects will be replicated in other materials or higher temperatures someday, and the experience won here will be important.
Regardless, it's cool to know it's been witnessed.
Observed. See. But no picture?
I agree. There are some pictures in the preprint https://arxiv.org/ftp/arxiv/papers/2202/2202.02798.pdf
(also https://www.weizmann.ac.il/condmat/superc/sites/condmat.supe... linked by klyrs in other comment)
The most relevant sentence is
> The images were acquired with a pixel size of 13 nm, acquisition time of 40 ms/pixel, and image size of 430 × 305 pixels.
Skip the text and look at figure 1, 2, 3, 4.
The left column is the experimental data. The center column is the same image using a simulation. The right column is the same simulation showing the flow with arrows instead of shadows of red/blue.
Figure 1 is made with gold. It's the normal behavior. When the electrons go up in the central "tube", they also go up in the "ears". Red means to the right and blue to the left.
Figure 2 is made with a very very very pure superconductor. It's the strange new behaviors. When the electrons go up in the central "tube", they spin in the "ears". Note that the position of the red and blue parts are reversed. They only measured the red/blue values, and later fit the arrows in the simulation.
The most relevant sentence is
> The images were acquired with a pixel size of 13 nm, acquisition time of 40 ms/pixel, and image size of 430 × 305 pixels.
Skip the text and look at figure 1, 2, 3, 4.
The left column is the experimental data. The center column is the same image using a simulation. The right column is the same simulation showing the flow with arrows instead of shadows of red/blue.
Figure 1 is made with gold. It's the normal behavior. When the electrons go up in the central "tube", they also go up in the "ears". Red means to the right and blue to the left.
Figure 2 is made with a very very very pure superconductor. It's the strange new behaviors. When the electrons go up in the central "tube", they spin in the "ears". Note that the position of the red and blue parts are reversed. They only measured the red/blue values, and later fit the arrows in the simulation.
"See" does not imply "with eyeballs"
While "see" seems like the obvious default sensory analogy to use for "detect" with a SQUID, now that I think about it, maybe it's more a synaesthestic blend of seeing, feeling and hearing.
The linked page has one. It is beautiful. What else do you want?
The best you would get is a diagram. In physics "observed" does not necessarily mean, in fact usually does not mean, seen in the sense of looking at the effect visually.
Observed via a sensor. Such as a microphone can observe a beep, or an accelerometer can observe a bump.
With a title like that I’d expect a picture, I guess the definition of seeing is different :)
[deleted]
arXiv link to paper:
https://arxiv.org/abs/2202.02798
Shouldn't the repelling nature of electrons make this completely different from regular fluid flow?
The electrons are in a metal but also, particles in a fluid repel each other as well. A great deal of the macroscopic behaviour of everyday objects is (in part) a consequence of electrons repelling each other.
MIT news releases are getting more and more ridiculous.
A colleague was asking about fluid dynamics, relating to air flowing through a tube with a cylinder in the middle. The equations looked very similar to those used for coaxial cables, and someone else had commented that the physics models are in fact quite similar.
I can't find the StackExchange link right now, but here's another article about electron viscosity, "negative resistance, electron whirlpools and superballistic flow."
https://www.manchester.ac.uk/discover/news/graphene-reveals-...