MIT scientists have coaxed atoms into an exotic “edge state” for the first time, allowing them to flow completely friction-free. The breakthrough could lead to better superconductor materials.
As electrons move through different materials, they encounter different levels of resistance. Basically, insulators allow little to no movement, semiconductors allow some, conductors allow a lot, and superconductors allow total freedom of movement with no resistance. As such, superconductor materials could be used for high-speed data and energy transmission, while the strong electromagnetic field they produce would enable levitating high-speed transport.
The problem is, studying the movement of electrons is tricky business, because these particles are tiny and move super fast. So for the new study, the MIT team found a way to coax atoms, which are much larger and slower, to perform the same behavior.
Specifically, the researchers were studying a type of superconductivity called edge states. In certain materials, electrons don’t move freely through the whole material but are confined to the edges, where they flow without any friction whatsoever. Even when obstacles are placed in their path, they skirt around them effortlessly, rather than bouncing off like they normally would.
In electrons, these states occur over femtoseconds (quadrillionths of a second), and distances of fractions of a nanometer, which of course is hard to capture. But atoms make that far more visible.
“In our setup, the same physics occurs in atoms, but over milliseconds and microns,” said Martin Zwierlein, co-author of the study. “That means that we can take images and watch the atoms crawl essentially forever along the edge of the system.”
The researchers confined a cloud of around a million sodium atoms to a laser trap, at temperatures of a hair above absolute zero, and spun them around in circles super quickly.
“The trap is trying to pull the atoms inward, but there’s centrifugal force that tries to pull them outward,” said Richard Fletcher, co-author of the study. “The two forces balance each other, so if you’re an atom, you think you’re living in a flat space, even though your world is spinning. There’s also a third force, the Coriolis effect, such that if they try to move in a line, they get deflected. So these massive atoms now behave as if they were electrons living in a magnetic field.”
Then, they introduced the edge – a ring of laser light that made a kind of wall around the outside. When the atoms touched the ring, they were found to stick to it, flowing freely along that edge in one direction.
Next, the researchers introduced some speed bumps to see how the atoms handled it. They shone points of light into the ring, and sure enough, the atoms continued unperturbed.
“We intentionally send in this big, repulsive green blob, and the atoms should bounce off it,” said Fletcher. “But instead what you see is that they magically find their way around it, go back to the wall, and continue on their merry way.”
All up, the atoms’ behavior tracks with how electrons behave in edge states, making it directly visible for the first time. Scientists can now use this model to test new theories and learn more, which could help inform better superconductors.
“It’s a very clean realization of a very beautiful piece of physics, and we can directly demonstrate the importance and reality of this edge,” said Fletcher. “A natural direction is to now introduce more obstacles and interactions into the system, where things become more unclear as to what to expect.”
The research was published in the journal Nature Physics.
Source: MIT
