Shot noise reveals electron pairs in copper superconductors before transition

Physicists have used tiny fluctuations in electrical current to detect electron pairs in a copper-based superconductor before it becomes superconducting. The finding offers evidence that the material’s puzzling “pseudogap” may be linked to electron pairing, helping clarify a longstanding question about how cuprates can superconduct at relatively high temperatures.

The team, led by Milan Allan and Ingmar Swart, studied BSCCO crystals with a scanning tunnelling microscope, measuring shot noise as current passed between its tip and the sample. Pairing makes the noise stronger because paired electrons carry more charge, but the signal in cuprates is weak because single electrons also flow. The researchers compared noise at different energies with the energies where electrons appear to be missing; the article says the instrument took years to refine, but its text ends before reporting the detailed results.