The alternative to superconductors: the ‘limit state’ of electrons brings almost infinite energy closer

Normally, electrons are free particles They can move in any direction through most metals. However, when they encounter an obstacle, these negatively charged particles experience friction and disperse randomly, similar to how billiard balls bounce when colliding with each other.

However, in certain materials, electrons can behave as if they were flowing with a defined purpose. In these cases, they can get caught on the edges of the material and move in a single direction, following the limiting line. In this ‘edge state’, electrons flow without friction, sliding smoothly around obstacles while maintaining their trajectory around the perimeter.

They look very similar, but they are not superconductors

Unlike superconductors, where all electrons in a material move without resistance, in the ‘edge state’ current is generated only at the boundary of the material. Recently, physicists at MIT have managed to directly observe this edge state in a cloud of ultracold atoms. For the first time, the team has captured images of atoms moving without resistance along a boundary, even when encountering obstacles in their path.

They first resorted to the idea of ​​edge states to explain a curious phenomenon, today known as the quantum hall effectwhich was first observed in 1980 in experiments with layered materials, where electrons were confined in two dimensions. These experiments were carried out in ultracold conditions and under a magnetic field. When attempting to send a current through these materials, scientists noticed that the electrons did not flow directly through the material, but instead accumulated on one side in exact quantum quantities.

To try to explain this phenomenon, physicists introduced the idea that Hall currents are carried by edge states. They proposed that, under the influence of a magnetic field, electrons in an applied current could be deflected toward the edges of a material, where they would flow and accumulate in a way that could justify the initial observations.

“The way charge flows under a magnetic field suggests the existence of edge modes,” explains Richard Fletcherco-author of the study and associate professor of physics at MIT. “However, actually observing them is something quite special, as these states occur in femtoseconds and fractions of a nanometer, which is incredibly difficult to capture.”

Instead of trying to trap electrons in a limit state, Fletcher and his team realized they could recreate the same physics in a larger, more observable system. The group has been investigating the behavior of ultracold atoms in a carefully designed configuration that mimics the physics of electrons under a magnetic field.

“In our system, the same physics occurs in atoms, but in milliseconds and microns,” he explains. Martin Zwierleinphysics teacher. “This means we can image and watch atoms drift almost indefinitely around the edge of the system.”

These results, published in Nature Physicsoffer scientists new ways to manipulate electrons so that they flow frictionlessly, facilitating extremely efficient and lossless transmission of energy and data.

“We could imagine making small pieces of a suitable material and using them in future devices, allowing electrons to travel around the edges and connect the different parts of a circuit without losses,” explains Fletcher.

This is how the study was done

The team worked with a cloud of approximately one million sodium atoms enclosed in a laser-controlled trap and cooled to nanokelvin temperatures. Then, they manipulated the trap to spin the atoms, as if they were passengers on an amusement park Gravitron.

“The trap tries to pull the atoms toward the center, but there is a centrifugal force that pushes them out,” explains Fletcher. “Both forces balance each other, so that, from the perspective of an atom, it appears to live in flat space, even though its surroundings are spinning. In addition, there is a third force, the Coriolis effect, which makes it so that, if try to move in a straight line, they deviate. So, these massive atoms behave as if they were electrons in a magnetic field.”

In this artificial reality, researchers They introduced a ‘border’ in the form of a ring of laser light, creating a circular wall around the rotating atoms. When imaging the system, the team observed that when atoms encountered the ring of light, they flowed along its edge in a single direction.

“You can imagine it like marbles that you’ve spun rapidly in a bowl, continuing their motion around the edge,” says Zwierlein. “There’s no friction, no slowing down, no scattering of atoms in the rest of the system. There’s just a beautiful, coherent flow.”

“These atoms flow without friction for hundreds of microns,” adds Fletcher. “Flowing for so long without dispersing is a type of physics not generally observed in ultracold atomic systems.”

This effortless flow was maintained even when The researchers put up an obstacle in the path of the atoms, represented by a point of light that they projected along the edge of the original laser ring. Despite encountering this new obstacle, the atoms did not slow their flow or dispersebut rather they slid without friction as they normally would.

“We intentionally sent out this big icky green blob, and the atoms should bounce off it,” Fletcher says. “But instead, we watch as they magically find their way around it, return to the wall, and merrily continue their journey.”

The team’s observations on atoms document the same behavior that had been predicted for electrons. Their results show that the configuration of atoms is a reliable model to study how electrons would behave in extreme states.

“It is a clear realization of a very beautiful aspect of physics, and we can directly demonstrate the importance and reality of this advantage,” Fletcher says. “A natural direction is now to introduce more obstacles and interactions into the system, where things become more complex in terms of what to expect.”