A new theoretical study sheds fresh light on the relationship between superconductivity and “excess” electrons in materials known as electrides. The study, on a monolayer of aluminium hydride, shows that this material should be a conventional superconductor with a critical transition temperature TC of 38 K – the highest known transition superconducting temperature among all two-dimensional electrides reported to date.

Electrides are a type of exotic ionic solid that contain more electrons than expected from classical (valence bond) theory. These additional electrons are known as interstitial anionic electrons (IAEs) because they are not bound to any atoms. Instead, they are trapped in voids within the material’s crystalline lattice.

Theory suggests that manipulating these IAEs could offer a new route to modulating a material’s electronic properties. Another, even more tantalizing possibility is that IAEs could interact more strongly with vibrations of the crystal lattice (phonons) than “normal” electrons do, which would lead to superconductivity.

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