Niobium is a metal that, when cooled to a few degrees above absolute zero, conducts electricity without resistance. In labs, it is deposited as thin strips onto a substrate, like frosting on a cake. But during deposition, oxygen from the special mask seeps into the metal, and it spoils the superconducting properties.
The researchers fabricated niobium wires of various widths and thicknesses and measured how they transition to the superconducting state. It turned out that the temperature at which the metal fully loses resistance drops as the width decreases. Meanwhile, the temperature at which the transition begins stays the same. So the transition stretches out: part of the wire is already superconducting while part is not yet.
The cause is oxygen that diffuses from the resist (the mask material) into the niobium during sputtering. In narrow wires, the fraction of contaminated metal is larger, so the effect is more pronounced. Knowing this, engineers can tune fabrication conditions to reduce oxygen uptake, and then hybrid niobium-based devices could operate at temperatures above 2 kelvin, simplifying the creation of quantum computers.
Niobium is used in the superconducting magnets of MRI scanners: it's what allows strong magnetic fields to be generated without energy loss.
In Liu Cixin's novel 'The Three-Body Problem,' superconducting materials help create incredible technologies, but their properties depend heavily on purity and structure.