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Stack two layers of graphene, twisted at slightly different angles to each other, and the material spontaneously becomes a superconductor. Science still can't explain how something so magical can happen, but physicists use special equipment to reveal what is taking place under the surface.

Superconductivity is a subject that has intrigued scientists for generations, since it was first noted more than 100 years ago, in the Leiden laboratory of Nobel Prize winner Heike Kamerlingh Onnes. He cooled mercury to near absolute zero and suddenly, all resistance disappeared. If you introduce an electric current to such a cold metal, it will continue to flow until the cooling is stopped.

Cooling in this case means a temperature of around 270 degrees below zero, the temperature at which helium becomes liquid. This is complicated and expensive, so practical applications of superconductivity were limited to the magnets in MRI scanners in hospitals, up till now.

In the meantime, physicists have been searching for 'warm' superconductors which will operate with less cooling. For example, ceramic materials have been developed which are superconducting at minus 140. That's progress, but we're not there yet. There are still a lot of unanswered questions. What exactly happens inside those materials is one such question to which Leiden researchers Tjerk Benschop and Sense Jan van der Molen hope to find an answer.

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