An SEM image of the superconducting nanowires.
An SEM image of the superconducting nanowires.

A collaboration between experimental physicists at Saarland University and the Leibniz Institute for New Materials has produced a new ultrathin film that offers superconducting properties, and which could lead to a range of applications in aerospace and medical technology. The team showed that, at a temperature below around –200°C, their thin and flexible nanomaterial was able to conduct electricity without loss, as well as levitate magnets and screen magnetic fields.

The study, which was reported in the journal Superconductor Science and Technology [Zeng et al. Supercond. Sci. Technol. (2017) DOI: 10.1088/1361-6668/aa544a], demonstrated superconducting nanowires that can be woven into an ultra-thin film, suggesting an effective approach to the nanowire synthesis of high-temperature superconductors. The material comprises a fabric of plastic fibers and high-temperature superconducting nanowires, making it extremely pliable and adaptable. It is also very light, much less than a conventional superconductor, making it useful for applications where weight can be an issue as an alternative to many superconducting materials, which tend to be rigid, brittle and dense.

"Theoretically, the material can be made to any size. And we need fewer resources than are typically required to make superconducting ceramics, so our superconducting mesh is also cheaper to fabricate."Uwe Hartmann

Superconducting granular Bi-2212 nanowires were synthesized by electrospinning, a technique more common in making high-yield polymer micro-fibers. A liquid material was then pushed through a fine nozzle to which a high electrical voltage was applied, offering nanowire filaments of around 300 nanometers. They then heated the mesh of fibers to ensure superconductors of the correct composition were produced, with the superconducting material typically being an yttrium barium copper oxide compound.

As superconductors tend to have no electrical resistance at extremely low temperatures, and can therefore conduct an electric current without loss, the material’s electrons are able to flow unrestricted through the cold immobilized atomic lattice. With no electrical resistance, when a magnet comes near to a cold superconductor, it effectively “sees” a mirror image of itself in the superconducting material. If a superconductor and a magnet are placed in close proximity and cooled using liquid nitrogen, they therefore repel each another and the magnet levitates above the superconductor. However, if the temperature is too high, frictionless sliding will not occur.

The material could become a replacement for superconducting powder for coating materials. Although nano or micro particulate powder always forms bigger clusters, thus losing their properties, in this nanowire network this is not a concern due to the particularity of the structure. The physicists are now looking to make a wider application of the synthesis of cuprate superconducting nanowires by electrospinning to investigate how to decrease the treatment temperature to obtain the superconducting phase, as this could help maintain the structure of the nanowires.