During the STSM of Vladimir Fomin (Moldova State University and Leibniz IFW Dreden) to the Vienna University, jointly with Oleksandr Dobrovolskiy and his collaborators, we analyzed the optimal geometries and physical conditions towards investigation of topologically nontrivial states in transport in superconductor open nanotubes, which have paraxial slits with metal contacts carrying transport current. Our analysis, in which also Igor Bogush (Moldova State University) actively participated, led to unveiling of several different vortex patterns that appeared in superconductor open nanotubes even without edge defects, due to the inhomogeneity of the normal magnetic induction component. If the magnetic field was directed such that maximal magnitudes of the normal magnetic field were symmetric with respect to the slit, then there were two symmetric vortex jets or chains moving in opposite directions. The crossing of the half-tubes by dc-driven vortices induced GHz-frequency voltage oscillations with spectra evolving between sharp lines and a blurred noise in certain ranges of currents and fields. One of the spectral lines corresponded to the vortex nucleation rate. Fractional parts of the latter were attributed to the number of trajectories that were passed by vortices. Integer multiples of the lines appeared due to the non-linearity of the system. A blurry spectrum implied a complex vortex arrangement because of the multifurcations of their trajectories. Due to a stronger confinement of single vortex chains in tubes of small radii, jumps in the average voltage and frequency of microwave generation were revealed, which occurred when the number of fluxons moving in the half-tubes increased by one. In all, our findings are essential for novel 3D superconductor nanodevices, which can operate in few- and multi-fluxon regimes.
The results of the collaborative work during the STSM supported by the E-COST-GRANT-CA21144-d8436ac6-b039a83c-fa29-11ed-9946-0a58a9feac02 have been presented in the paper http://arxiv.org/abs/2311.02946.
