Threading flux through helixes

The fabrication and understanding of complex three-dimensional (3D) architectures on a nanoscale is one of the promising routes towards new schemes for a next generation of advanced electronic devices. This endeavour requires advanced new processing technologies, state-of-the-art structural and electronic characterization experiments and advanced theoretical models.

In this work, a team of researchers from Zaragoza, Paris, Madrid, Dresden and Nijmegen have investigated the superconducting properties of 3D tungsten carbide nanohelices. They were fabricated by means of He+ focused-ion-beam microscopy in combination with a precursor gas. The helices with pitches between 200 nm and 2.3 μm, diameters from 100 to 295 nm consist of nanowires as thin as 45 nm.

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(a) Temperature dependence of the critical field of a tungsten carbide nanohelix in a perpendicular magnetic field. The values for Hc2 and Hmin are determined from R vs. T and R vs. B sweeps as the points where the resistance reaches 90 % and 10 % of the normal-state resistance R. The inset shows a scanning-electron-micrograph of the structure.

(b) Dependence of Hc2 on the angle between the helix axis and the applied magnetic field at 4 K, see inset in (a).

At low temperatures (T < 7 Kelvin / - 266 °C) these nano-helices display superconductivity with a large critical magnetic field (up to 15 Tesla) depending on the direction of the field with respect to the helix axis. This suggest that the geometry of the helices and their orientation in a magnetic field play a significant role in the superconducting phase transition, which can be qualitatively explained using an approach for the properties of thin-film superconductors. In this respect, the results can therefore form an important starting point for a fully quantitative 3D modelling of superconducting nanohelices with dimensions comparable to or smaller than the superconducting penetration depth.

Eventually, as a more general perspective, the peculiar superconducting properties of novel nanostructures may then pave the way towards promising new device applications and such as sensors, energy storage elements, and nano-antennas.

Related publication

Three-Dimensional Superconducting Nano-helices Grown by He+Focused-Ion-Beam Direct Writing, Rosa Córdoba, Dominique Mailly, Roman O. Rezaev, Ekaterina I. Smirnova, Oliver G. Schmidt, Vladimir M. Fomin, Uli Zeitler, Isabel Guillamón, Hermann Suderow and José María De Teresa, Nano Lett. 19, 8597 (2019)


Uli Zeitler