What is the normal charge of atoms?

When electrons can attract each other

The same charges repel each other, dissimilar charges attract each other. This basic principle of electrostatics is described by what is known as Coulomb's law. Accordingly, negatively charged particles such as electrons repel each other. In the journal “Nature”, however, researchers now report that electrons can also attract each other under certain conditions. The team was able to demonstrate this unusual behavior with a special structure made of nanotubes, thereby confirming a theory that was set up fifty years ago.

Schematic representation of the experiment

The research group around Assaf Hamo from the Weizmann Institute for Science in Rechovot, Israel, integrated two electrons into one carbon nanotube and one molecule into a second. The nanotubes have almost no defects. “This enables us to have good control over the individual electrons,” says team member Ilanit Shammass from the Weizmann Institute for Science. Assaf and colleagues had produced the molecule used artificially, as in this way they knew and could influence its electrical properties. In terms of its basic structure, it corresponds to two atoms between which an electron moves.

At temperatures close to absolute zero, the researchers placed the two nanotubes perpendicular to each other and then pushed them within a hundred nanometers of each other. The free electron in the molecule was repelled by one of the other electrons by the Coulomb force in such a way that it left a region with a positive charge in the molecule. This region attracted the two electrons in the neighboring nanotube. This created an attractive effect between the two. “The region in the molecule causes an electron to appear positively charged. This attracts the other electron, ”explains Shammass.

The fact that electrons attract each other and form pairs, so-called Cooper pairs, is a key requirement for superconductivity. This effect can be created by various methods. A purely electronic attraction, as the physicist William Littles described it fifty years ago, has never been observed experimentally before. So far, very low temperatures have always been necessary for this pair formation, also in this experiment. "One of the perspectives of our work is to construct new types of superconductors that can also work at higher temperatures," says Shammas.