Flux Manipulation in Nanostructured Ceramic Superconductors
The manipulation of magnetic flux via patterning represents one of the most challenging research areas in the field of today’s superconductivity. Nanoscale confinements of quantized flux (vortices) and directed vortex motion enable novel functionalities and new applications. Superconducting nano-and micro-devices based on the action of magnetic flux (so called fluxons) represent the basic elements for new fluxonic applications ranging from fluxon electronics and optics to fluxon quantum computing. In the framework of a European cooperation researchers at the University of Oslo and the Forschungszentrum Jülich have analyzed the guidance and mobility of vortices in nanostuctured high-temperature superconductors using a combination of electronic measurements, visualization of magnetic flux and simulation. The results are now published in 2 reviews.
Regimes of flux transport at microwave frequencies in nanostructured high-Tc films
R. Wördenweber, E. Hollmann, J. Schubert, R. Kutzner, and G. Panaitov
Abstract: We report on combined dc and microwave electronic measurements of magnetic flux transport in micron and submicron-patterned high-Tc films. In a given temperature regime below the superconducting transition temperature Tc, the current-driven flux transport is restricted to flux motion guided by the submicron patterns. Via frequency-dependent measurements of the forward transmission coefficient S21 it is demonstrated that the mechanism of the guided flux transport depends on the microwave frequency and the geometrical size of the superconducting structures. At low frequencies, flux is transported via Abrikosov vortices leading to additional microwave losses. Above a geometrically defined frequency, a different mechanism seems to be responsible for flux transport that does not contribute to the microwave losses and most likely represents a phase-slip type mechanism. The limiting vortex velocity obtained from the frequency dependence of the microwave properties agrees with the Larking-Ovchinnikov critical vortex velocity that is determined via dc pulse measurements. In spite of the change of mechanism, guidance of flux persists in these nanopatterns up to high frequencies of several GHz.
published: 3 February 2012
Mechanism for flux guidance by micrometric antidot arrays in superconducting films
J. I. Vestgården, V. V. Yurchenko, R. Wördenweber, and T. H. Johansen
Abstract: A study of magnetic flux penetration in a superconducting film patterned with arrays of micron-sized antidots (microholes) is reported. Magneto-optical imaging (MOI) of a YBa2Cu3Ox film shaped as a long strip with perpendicular antidot arrays revealed both strong guidance of flux and, at the same time, large perturbations of the overall flux penetration and flow of current. These results are compared with a numerical flux creep simulation of a thin superconductor with the same antidot pattern. To perform calculations on such a complex geometry, an efficient numerical scheme for handling the boundary conditions of the antidots and the nonlocal electrodynamics was developed. The simulations reproduce essentially all features of the MOI results. In addition, the numerical results give insight into all other key quantities (e.g., the electrical field), which become extremely large in the narrow channels connecting the antidots.
published: 23 January 2012