The traditional Japanese basket weaving pattern kagomé (right) served as an inspiration for an array of fluxon traps produced with a helium-ion microscope in a high-temperature superconductor. The anchored fluxons are represented by blue figures, while the purple fluxons are trapped by their neighbors. Image: Bernd Aichner, University of Vienna.An international research team led by Wolfgang Lang at the University of Vienna in Austria has succeeded in producing the world's densest complex nano arrays for anchoring magnetic flux quanta, or fluxons, in superconductors. This was achieved by irradiating the superconductor with a helium-ion microscope at the University of Tübingen in Germany. The researchers, who report their work in a paper in ACS Applied Nanomaterials, were inspired by traditional Japanese basket weaving.
Superconductors can carry electricity without loss if they are cooled below a certain critical temperature. But in order to make pure superconductors suitable for most technical applications, defects need to be introduced into them. Until recently, these defects were randomly distributed, but nowadays researchers prefer the tailored periodic arrangement of these defects.
Such defects are important because a magnetic field can only penetrate into a superconductor as quantized portions, or fluxons. If the superconductivity is destroyed in very small regions, the fluxons because anchored at exactly these places. Periodic arrays of defects allow the creation of two-dimensional ‘fluxon crystals’, which are a model system for many interesting investigations.
The defects serve as traps for the fluxons, and by varying easily accessible parameters numerous effects can be investigated. "However, it is necessary to realize very dense defect arrangements so that the fluxons can interact with each other, ideally at distances below 100nm, which is a thousand times smaller than the diameter of a hair," explains team member Bernd Aichner from the University of Vienna.
Particularly interesting for researchers are complex periodic arrangements, such as the quasi-kagomé defect pattern investigated in the current study, which was inspired by traditional Japanese basket weaving. The bamboo stripes in a kagomé basket are replaced by a chain of defects with 70nm spacings. This allows the creation of approximately circular fluxon chains, which hold a free fluxon trapped in their midst. Such fluxon cages are based on the mutual repulsion of fluxons, and can be opened or locked by changing the external magnetic field. They are therefore regarded as a promising concept for the realization of fast, low-loss superconducting circuits.
This research was made possible by a novel device at the University of Tübingen – a helium-ion microscope -which the researchers used to produce the chain of defects. Although it has a similar operating principle to a scanning electron microscope, the helium-ion microscope offers a previously unmatched resolution and depth of field because of the much smaller wavelength of helium ions.
"With a helium-ion microscope, the superconducting properties can be tailored without removing or destroying the material, which enables us to produce fluxon arrays in high-temperature superconductors with a density that is unrivaled worldwide," emphasizes Dieter Koelle from the University of Tübingen. The scientists are now planning to further develop the method for even smaller structures and to test various theoretically proposed concepts for fluxon circuits.
This story is adapted from material from the University of Vienna, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.