What happens when an electron moves

physics : The shared electron

Electrons are considered indivisible elementary particles. To put it simply, they orbit atomic nuclei like planets around their parent star. However, under special conditions it can happen that electrons split into two parts. An international team of scientists around Justine Schlappa from the Helmholtz Center Berlin for Materials and Energy reports on this in the specialist journal "Nature". According to the researchers, this amazing mechanism could possibly be used in the future in the development of superconductors.

Electrons have certain properties such as an electrical charge and “spin”. The charge is negative and makes the particles the basic building blocks of all electronics. The spin describes the intrinsic rotation of the electron, which turns each particle into a tiny bar magnet with a north and south pole. This is important for the material properties: For example, if the north poles of all electrons point in the same direction, the material is magnetic.

“Normally, the charge and spin are inseparably linked in every electron,” says Ralph Claessen from the University of Würzburg, who wrote a comment on the study in “Nature”. “When a current flows in a wire, all electrons move with their spin and charge in the same direction.” But that changes when the wire becomes extremely thin and the particles can only move forwards or backwards. "Then quantum mechanical effects occur," says the physicist. "They lead to the fact that spin and charge are separated from one another and move as quasiparticles through the 'nanowire' at different speeds."

This long suspected effect was experimentally proven for the first time a few years ago. Schlappa and colleagues have now demonstrated another form of electron division. On the one hand, this creates the well-known quasiparticle that carries the magnetic information (called “spinon”). The second is called "Orbiton" and carries the information about the movement of the electron around the atomic nucleus.

The researchers used a particularly thin nanowire for their experiment. It consists of individual copper atoms that are arranged like a string of pearls in strontium copper oxide (Sr2CuO3). This material was cooled to minus 259 degrees Celsius and irradiated with intense X-ray light at the Swiss Paul Scherrer Institute.

In this way, individual copper electrons received additional energy. "This brought them into other orbits - so-called orbitals - in which they orbit the atomic nucleus faster," explains Jeroen van den Brink from the Leibniz Institute for Solid State and Materials Research Dresden. After this excitation, the electrons split into two quasiparticles, the spinon and the orbiton, which moved through the nanowire at different speeds. However, the new particles cannot leave the material.

In contrast to cells under the microscope, individual electrons and their division cannot be observed directly. They are much too small for that. The researchers base their statement on detectors that register traces of thousands of such decays. “We measure how the energy and the momentum of the X-ray radiation change when it hits the material,” explains van den Brink. The properties of the newly created particles can be derived from this. And they agreed pretty much with the theoretically predicted, as the Dresden physicist found.

So far, one can only speculate about the applications of the discovery. According to the researchers, it could be useful in high-temperature superconductivity. There it is a matter of transmitting electrical current without loss well above absolute zero. Since the electrons in copper-based superconductors behave in a similar way to those in strontium-copper-oxide, the physicists hope for new knowledge in order to come closer to the dream of a resistance-free current conductor.

Ralph Claessen brings another field into play. "Miniaturization continues in microelectronics," he says. At some point, transistors and the connecting lines in the computer chips would be so small that quantum mechanical effects could become effective. "As the experiment by Schlappa and colleagues shows, the electrons then no longer behave as we know them," says Claessen. "Whether the effect of the 'disintegration' of these particles can be used to manufacture new switching elements is an exciting question for future research."

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