Title: Superconductivity in Rolled-up Nanoarchitectures.
When: Thursday, June 07, (2018), 12:00.
Place: Department of Condensed Matter Physics, Faculty of Sciences, Module 3, Seminar Room (5th Floor).
Speaker: Vladimir M. Fomin, Institute for Integrative Nanosciences (IIN), Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Germany.
Advances in the high-tech fabrication methods have provided novel curved micro- and nanoarchitectures of superconductors, e.g., nanostructured microtubes, helical microcoils and their arrays. Their highly controllable superconducting properties as well as possible applications have been attracting increasing interest . Vortex dynamics in open superconductor microtubes thickness at nanoscsale in the presence of a transport current are determined by the interplay between the scalar potential and the inhomogeneous magnetic field component, which is normal to the surface. Rolling up superconductor Nb nanomembranes into open tubes and helical microcoils allows for a new, highly correlated vortex dynamics regime that shows a three-fold increase of a critical magnetic field for the beginning of vortex motion and a transition magnetic field between single- and many-vortex dynamic patterns. These results demonstrate pathways of tailoring nonequilibrium properties of vortices in curved superconductor nanoarchitechtures leading to their application as tunable superconducting flux generators for fluxon-based information technologies. Using an inhomogeneous transport current enables an efficient control over the branching of vortex nucleation periods and allows for a significant reduction of the average number of vortices that occur in the microtube per nanosecond. The related energy dissipation reduction is of importance for extension of the spectrum of superconductor-based sensors to the low-frequency range. The non-monotonic voltage generated by moving vortices as a function of magnetic field is revealed using FDTD-simulations for a Nb microtube made by roll-up technology, as distinct from a planar membrane of the same dimensions. Open superconductor tubes are shown to produce less dissipation as compared to the planar structures under the same magnetic field and transport current. The induced voltage as a function of the magnetic field provides information about the vortex pattern. In particular, an increase of the number of vortex chains in the tube results in a 6-fold decrease of a slope of the induced voltage as a linear function of the magnetic field . A three-fold increase of the magnetoresistance in its peak value at 10 mT occurs in an ultrathin Nb tube of radius 400 nm and length 5 𝜇m. This non-monotonic behavior is attributed to the occurrence of a phase slip area at such magnetic fields when the quasi-stationary pattern of vortices changes from single to double chains in each half-turn . The effect is promising for application design of novel superconductor switching-based detectors. In superconductor helical microcoils, the distribution and number of vortices in a quasi-stationary pattern can be controlled by the helical radius, pitch distance and stripe width . In the helical microcoils, quasi-degeneracy of vortex patterns, which emerges under the condition that the total number of vortices is incommensurable with the number of half-turns, opens up new possibilities for bifurcations and the related control of the vortex transport.
Snapshots of the order parameter at two external magnetic fields for the open tube with nm and jtr=50 GA/m2.
This work has been supported by the European COST Action no. CA16218 “Nanoscale Coherent Hybrid Devices for Superconducting Quantum Technologies”. I gratefully acknowledge fruitful discussions with D. Bürger, D. Grimm, R. P. Huebener, E. A. Levchenko, S. Lösch, E. A. Posenitskiy, R. Rezaev, O. G. Schmidt, E. I. Smirnova, H. Suderow, F. Tafuri, and R. Tidecks.
1. V. M. Fomin, in: A. Sidorenlko (Ed.), Functional Nanostructures and Metamaterials, Springer, Berlin – Heidelberg, 2018, 26 pp. (https://doi.org/10.1007/978-3-319-90481-8_10).
2. R. O. Rezaev, E. A. Posenitskiy, E. I. Smirnova, E. A. Levchenko, O. G. Schmidt and V. M. Fomin, Phys. Stat. Sol. Rapid Research Letters, 12 pp. (2018) (in press).
3. R. Rezaev E. Smirnova, E. Posenitskiy, E. Levchenko and V. Fomin, Verhandlungen der Deutschen Physikalischen Gesellschaft 3, 264 (2018).
4. V. M. Fomin, R. O. Rezaev, E. A. Levchenko, D. Grimm and O. G. Schmidt, Journal of Physics: Condensed Matter 29, 395301 (2017).