Vortex Matter in Rolled-Up Superconductor Micro- and Nano-Architectures
Abstract: Advances in the high-tech roll-up fabrication methods have provided novel curved superconductor micro- and nanoarchitectures (e.g., nanostructured microtubes, microhelices, and their arrays). Their superconducting properties and possible applications remain largely terra incognita. The combination of reduced dimensionality with the curved geometry of rolled-up superconductor micro- and nano-architectures is a rich source of novel vortex physics.
Numerical modeling with the time-dependent Ginzburg-Landau approach shows that the curved geometry governs the dynamics of vortices in the presence of transport currents in open superconductor micro- and nanotubes subject to a magnetic field orthogonal to the axis. The vortex dynamics are described by two characteristic times: the period of nucleation of vortices at one edge of the structure and the duration of motion of a vortex along the structure. Synergetic effects of curvature and dimensions cause drastic changes in both equilibrium and dynamical vortex patterns, which lead to a nonmonotonic dependence of characteristic times on the magnetic field.
Rolling superconductor niobium nanomembranes into open tubes and helical microcoils allows for a new, highly correlated vortex dynamics regime that reveals a surprising (by a factor of 3) increase in a critical magnetic field for the beginning of vortex motion and a transition magnetic field between single- and many-vortex dynamic patterns in an open nanotube. The dynamics of superconducting vortices in the upper and lower half-cylinders are strongly correlated in symmetric pure open tubes. The presence of pinning centers or inhomogeneous currents, which lift the symmetry of half-cylinders with respect to reflection in the plane that includes the tube axis and the centerline of the slit, reduces those correlations. The renormalization of the magnetic field in tubes of finite thickness and the evolution of the scalar potentials described by the Poisson equation are included in the analysis.
The voltage induced by the moving vortices in open microtubes is of the order of several mV. Open microtubes can serve as tunable superconducting vortex generators for fluxon-based information technologies. An inhomogeneous transport current, which is introduced through multiple electrodes in an open nanotube, leads to a controllable branching of the vortex nucleation period. The average number of vortices occurring in the tube per nanosecond can be effectively reduced by using the inhomogeneous transport current, which is important for noise and energy dissipation suppression in superconductor applications (e.g., for sensors operating at lower frequencies). For superconductor helical microcoils, the pattern and number of vortices in a stationary distribution are determined by their confinement to the ultrathin helical coil and can therefore be efficiently controlled by the helical geometry.