A thin film of zirconium nitride lies on a substrate. It was cooled to 0.5 kelvin, which is colder than outer space. In a magnetic field, the film's resistance did not change as expected for a bulk material. Instead, it behaved as if superconductivity existed only in a plane.

Inside the film, there are defects: some zirconium atoms are missing, and there is too much nitrogen. These defects break the order, so superconductivity cannot engulf the entire material. Instead, rare islands emerge where superconductivity still holds. Around them, the material is a normal metal.

By measuring resistance, the scientists saw that the curves for different temperatures do not converge at a single point. This is a hallmark of the Griffiths singularity. But the law by which resistance depends on field and temperature turned out to be two-dimensional. The superconducting islands seem to link into a flat network, like paths between puddles.

Previously, it was unclear whether this could happen in a three-dimensional superconductor with a cubic lattice. Now it is shown: yes, it can. Disorder from defects creates rare islands, and they arrange into an effectively two-dimensional structure. This deepens our understanding of quantum transitions, but there are no direct applications yet.