This New Phenomenon Squeezes Electrons to Speeds Physicists Didn't Even Know Were Possible

Now entering 'superballistic' mode.

11 MAR 2017

Imagine you've got 50 people all trying to squeeze through the same doorway at the same time. That stress-filled bottleneck would usually slow everyone down, but what if - somehow - that mob could actually get through faster than one person going through alone?

It sounds crazy, but that's what physicists have figured out how to do using electrons, demonstrating that under certain conditions, big groups of electrons can squeeze through a gap in a piece of metal faster than current physics could predict.


Referred to as a 'superballistic' flow, the newly discovered behaviour describes how groups of electrons can travel through tight spaces faster than a single electron, and it could lead to materials that can transmit electricity with almost no resistance.

That would be huge, because while superconductivity offers zero resistance - making it one of the most intriguing and potentially lucrative phenomena in physics - it can only be achieved at super-chill temperatures below 5.8 K (-267°C or -450°F).

If researchers can recreate this new superballistic flow of electrons in a conductive material, they could harness many of the benefits of superconductivity in the much-coveted room temperature environment.

Describing their new theoretical model of how electrons flow through tiny metal gaps, physicists from MIT found that large groups of electrons could actually 'coordinate' with each other to exceed what's been considered a fundamental speed limit for electrons in a tight space - known as Landauer's ballistic limit. 

"[W]e can overcome this boundary that everyone thought was a fundamental limit on how high the conductance could be," one of the team, Leonid Levitov, told David L. Chandler at MIT News.

"We've shown that one can do better than that."


When simulating the behaviour of electrons squeezing through a constricted opening, they were surprised to find that these subatomic particles actually resembled the known physics at work in gas particles passing through a tight spot.

If you watch gas pass through a constricted passageway on a molecular level, you'll see that individual particles will move at random, and are far more likely to hit the walls of the tunnel a few times along the way than they are to make a clean, perfectly unobstructed journey all the way through. 

And if you're bouncing off the walls as you go, you're losing energy, which slows down your progress every time.

"But with a bigger batch of molecules, most of them will bump into other molecules more often than they will hit the walls," says Chandler. 

"Collisions with other molecules are 'lossless', since the total energy of the two particles that collide is preserved, and no overall slowdown occurs."

That means there's a kind of 'safety in numbers' when it comes to protecting individual gas molecules from energy-wasting collisions. 

"Molecules in a gas can achieve through 'cooperation' what they cannot accomplish individually," Levitov says.

Not only that, but the laws of physics also dictate that when the density of the gas molecules in the tunnel increases, the pressure needed to push them through drops, giving the grouped molecules acceleration that individual molecules can't achieve. 

When Levitov and his team recreated this scenario using electrons and various metals - including everyone's favourite wonder material, graphene - they found that the electrons could move in a neatly coordinated way. 

This was completely unexpected, and broke the well-established Landauer's ballistic limit, making way for a new speed - superballistic.

"We ... see that electrons in a viscous flow can achieve through cooperation what they cannot accomplish individually," the researchers report in their paper.

"The reduction in resistance arises due to the streaming effect, wherein electron currents bundle up to form streams that bypass the boundaries, where momentum loss occurs. This surprising behaviour is in a clear departure from the common view that regards electron interactions as an impediment for transport."

So, what now? Well, given that the researchers have recreated the behaviour of gas in electrons - the things that power our electronic devices - the discovery points to electronics that could achieve high output with low power.

And unlike superconductivity, which achieves zero electrical resistance at the price of incredibly low temperatures that are expensive to achieve, this technique works at room temperature, and actually gets better the more you increase the temperature.

"[Superballistic flow] is assisted by temperature, rather than hindered by it," Levitov told MIT News.

The researchers admit that their work is so far purely theoretical, but point out that various aspects of its predictions have already been proven experimentally by previous studies.

And Stanford physicist David Goldhaber-Gordon, who was not involved in the research, says that actually testing these predictions experimentally would be entirely feasible in the lab using graphene. 

We'll have to wait and see if the team's calculations are correct, but superconductivity better watch its back - we just might have something even better on our hands.

The research has been published in Proceedings of the National Academy of Sciences.

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