Looking inside superconductors

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.

Understanding how the atomic structure of a material gives rise to superconductivity remains a major challenge in condensed-matter physics. The study, published in Physical Review Letters and led by researchers from the Department of Chemistry at the University of Warwick working with the ESRF, 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. Cuprate superconductors have been studied for decades, yet questions remain about how structural variations within these materials influence their macroscopic properties.

Challenging a long-standing assumption

For 40 years, most theories about how cuprates work have assumed their crystal structure is the same all the way through, despite evidence that structural heterogeneity can occur. What had remained unresolved was how these different structures are organised throughout the bulk of the material. Using a technique at beamline ID11 called scanning 3D X-ray diffraction, which is similar to a medical CT scan but probes the arrangement of atoms inside a crystal, the researchers were able to build a three-dimensional picture of this previously inaccessible structural organisation.

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 (see image below). These boundaries were so wide that they behaved almost like a structure in their own right, rather than a simple dividing line.

3D X-ray reconstruction revealing the previously unresolved organisation of different crystal structures throughout a 214 cuprate superconducting material. Dark regions have the expected structure, while lighter regions show a different structure. The boundary regions between them are approximately 150 nm wide.

"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," said Professor Mark Senn, of the University of Warwick's Department of Chemistry, who led the study. "The crystal is fundamentally patchworked and textured, with unusually wide boundary regions that likely work against superconductivity rather than just sitting alongside it."

Implications for superconductivity

The findings could help explain why superconducting properties vary between apparently similar materials and suggest that some existing measurements of bulk properties may need to be reconsidered. They also point to the need for theoretical models that account for the previously hidden structural complexity of these materials. 

The researchers suggest that similar structural behaviour could occur across the wider family of cuprate superconductors, and possibly in other related materials being investigated for superconductivity under extreme pressure. 

Revealing hidden structure in 3D

The study also demonstrates the potential of scanning 3D X-ray diffraction at ID11 to reveal structural variations hidden within the bulk of complex materials. By resolving crystal structures in 3D, at a level of detail not previously possible, the technique offers a new way to investigate how microscopic structural features influence the macroscopic properties of materials.

"This experiment was only possible thanks to the ESRF’s Extremely Brilliant Source upgrade," explained Jonathan Wright, beamline scientist at ID11. "Achieving the highest resolution at several temperatures required the increased flux, together with the Dectris CdTe detector. We are now working on a refurbishment of ID11 to further improve strain and spatial resolution for this new type of X-ray diffraction microscopy."

Reference
Giant Domain Walls and Intrinsic Heterogeneity in 214 Cuprate Superconductors, E. Ladbrook et al., Physical Review Letters 137, 126504 (2026); https://doi.org/10.1103/r62x-kt5j