🧲 This crystal becomes superconducting when compressed

A crystal made of very thin layers changes profoundly when compressed. Under high pressure and near absolute zero, it becomes superconducting. Current can then flow through it with no measurable electrical resistance. This change occurs precisely when the material's magnetic ordering disappears, a connection that intrigues physicists.

The material studied is called CeSiI. At normal pressure, it already conducts electricity and has well-ordered magnetic behavior. But it only becomes superconducting at an extremely low temperature. The maximum measured is around -272.9 °C, i.e. 0.24 K, just 0.24 °C above absolute zero.

Its structure resembles a stack of sheets that are quite weakly bound to each other. This organization allows studying behaviors close to those of two-dimensional materials. CeSiI also belongs to a family where interactions between electrons are particularly strong. The mobile electrons react to the tiny magnets carried by certain atoms.

At normal pressure, these tiny magnets align in a precise order: neighbors point in opposite directions. This is called antiferromagnetism. By gradually compressing the crystal, the researchers found that this order weakens, then disappears around 6 GPa. This pressure corresponds to about 60,000 times the atmospheric pressure at sea level.

It is near this disappearance of antiferromagnetism that superconductivity appears. This proximity is interesting, as it can shed light on how electrons pair up. In an ordinary superconductor, this pairing depends mainly on the vibrations of the crystal's atoms.

The researchers thus have a single material where pressure, magnetism, and superconductivity can be tuned together. CeSiI can notably be separated into very thin layers, which will allow these interactions to be studied as the thickness decreases. The next experiments will seek to determine more precisely which mechanism pairs electrons and produces superconductivity in this magnetic environment.