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It is one of the more counter-intuitive stunts in the repertoire of scientists who study superconductivity. Stack two mat­erials, even insulators, on top of one another and voilà: a dramatic drop in electrical resistance can emerge between them. The negligible resistance of superconducting materials, sought for applications such as highly efficient electric grids, typically emerges at temperatures close to absolute zero — and only in certain materials. But physicists have shown that the stacking effect, called interface superconductivity, can occur at temperatures up to almost 80 kelvin.

Now, a researcher says that interface superconductivity can exist in a single crystal of an iron-based superconductor. The discovery will rejuvenate work on a family of compounds that first showed high-temperature superconductivity in 2008, but in recent years had seemed to disappoint.

“This is something conceptually very new,” says Anvar Zakhidov, a physicist at the University of Texas at Dallas. “It raises fundamental questions that people will jump on.”

The provocative result comes from a superconducting pioneer: Paul Chu of the University of Houston in Texas. In the 1980s, he helped to discover the first high-temperature superconductors, a family of copper-containing compounds (see ‘All in the family’). In a paper posted on the arXiv preprint server on 30 August1, Chu and his colleagues now report their work on an iron-based crystal that generally superconducts at 30 kelvin — but that contains small regions that superconduct at 49 kelvin. Chu proposes that the effect is the result of many interfaces forming tens of nanometres apart within these regions (see ‘At the interface’).

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