Scientists have shown that a material treated for 40 years as a uniform, textbook superconductor is in fact a patchwork of different crystal structures throughout its bulk, using one of the latest 3D imaging techniques to see deep inside the crystal for the first time.
High-temperature superconductivity is widely regarded as one of the most significant scientific discoveries of the past 40 years. It promises technologies built on electricity that flows with zero resistance and magnets far more powerful than anything possible today, and underpins research into future power grids, medical scanners, and quantum computers.
The study, published in Physical Review Letters and led by researchers in the Department of Chemistry at the University of Warwick working with the European Synchrotron Radiation Facility (ESRF) in France, looked inside a type of superconductor called a cuprate, a copper-based material that can carry electricity with no resistance at unusually high (though still very cold) temperatures.
For 40 years, most theories about how cuprates work have assumed their crystal structure is the same all the way through. Using a technique called scanning 3D X-ray diffraction, which works a bit like a medical CT scan but for the arrangement of atoms inside a crystal, the team was able to build a three-dimensional picture of the material's interior for the first time.
What they found was a crystal divided into regions with two subtly different atomic arrangements, separated by boundaries hundreds of times wider than anyone expected to see between two crystal structures. These boundaries were so wide that they behaved almost like a structure in their own right, rather than a simple dividing line.
Professor Mark Senn, of the University of Warwick's Department of Chemistry, who led the study, said: "For forty years, the working assumption has been that these materials are the same all the way through, and nearly all the theory is built on that picture. We've shown it doesn't hold. The crystal is fundamentally patchworked and textured, with unusually wide boundary regions that likely work against superconductivity rather than just sitting alongside it.
"This might explain why some materials perform better than others and means some existing bulk measurements will need to be reinterpreted and future theoretical models built that incorporate this structural complexity."
The team believes this kind of hidden structure is likely common across the wider family of cuprate superconductors, and possibly in other related materials being explored for superconductivity under extreme pressure. They also see the method itself, enabled by a recent 150M euro upgrade to the ESRF, as a breakthrough: it opens up the ability to look inside a wide range of materials in 3D, at a level of detail not previously possible, to understand how their internal structure shapes the way they behave.
