Superconductivity is when electric current flows without losses, like water through a perfectly smooth pipe. It usually occurs at very low temperatures, but there are materials where it appears at higher ones. One path to this is through so-called flat bands: regions in the energy spectrum where electrons barely move but interact strongly with each other.
In the new work, scientists took the Lieb lattice, a simple model that has a flat band, and switched on attraction between electrons. They used diagrammatic Monte Carlo: it's like a computer simulation that makes no approximations and honestly accounts for all possible interactions. It turned out that the pair response (a measure of how ready electrons are to form pairs) grows linearly as temperature drops. This means superconductivity sets in abruptly, like a phase transition, not gradually.
The highest T* occurs when three energy bands touch at a single point. It's like three roads converging at one intersection: electrons find it easier to switch from one to another, and superconductivity is enhanced. Perhaps such band-touching points are the key to creating superconductors that work at room temperature.
In a flat band, electrons barely move, but it is precisely their 'stillness' that strengthens the interaction leading to superconductivity.