An ordinary superconductor loses resistance when cooled, and current flows through it without loss. But in ultrathin films, things are different: the material fluctuates between normal and superconducting states, and in this transition zone, strange resistance waves emerge. Resistance rises and falls as if someone were turning a volume knob.
The authors of the study took several layers of NbSe₂ — a material that becomes superconducting at very low temperatures. They did not carve any rings into it, but they observed characteristic resistance oscillations in a magnetic field. These oscillations resemble light interference: waves overlap and either amplify or cancel each other. Here, it is the quantum waves of electrons that interfere.
This discovery provides a new tool: instead of complex lithography, natural inhomogeneities in thin films can be used. And it is a step toward understanding how superconductivity breaks down in the two-dimensional world.
NbSe₂ is a layered material: it can be split into sheets one atom thick, like graphite in a pencil.