This study proposes a novel solution blow spinning technique (SBS) for fabricating YBCO ceramic nanofibers. The precursor solutions were obtained from Y, Ba, and Cu metallic acetates (Ac) and poly(vinyl pyrrolidone) (PVP, Mw = 360,000). Ac:PVP concentrations of 1:1 and 5:1 were tested, resulting in ceramic nanofibers with average diameters of 359 and 375 nm, respectively. X-ray diffraction confirmed the formation of a pure phase of YBa2Cu3O7-x. This is the first study to use SBS for fabricating YBCO nanofibers, and this technique shows promise for obtaining high-quality ceramic materials.

We have established a link between the global ac response and the local flux distribution of superconducting films by combining magnetic ac susceptibility, dc magnetization, and magneto-optical measurements. The investigated samples are three Nb films: a plain specimen, used as a reference sample, and other two films patterned with square arrays of antidots. At low temperatures and small ac amplitudes of the excitation field, the Meissner screening prevents penetration of flux into the sample. Above a certain ac drive threshold, flux avalanches are triggered during the first cycle of the ac excitation. The subsequent periodic removal, inversion, and rise of flux occurs essentially through the already-created dendrites, giving rise to an ac susceptibility signal weakly dependent on the applied field. The intradendrite flux oscillation is followed, at higher values of the excitation field, by a more drastic process consisting of creation of new dendrites and antidendrites. In this more invasive regime, the ac susceptibility shows a clear field dependence. At higher temperatures a smooth penetration occurs, and the flux profile is characteristic of a critical state. We have also shown that the regime dominated by vortex avalanches can be reliably identified by ac susceptibility measurements.

The demand for nanostructured materials can increase exponentially due to the miniaturization of devices and their potential application in different areas, such as electronic and medicine. Therefore, high production rates are essential for making nanomaterials commercially available. When electrospinning (ES) and solution blow spinning (SBS) are employed for producing ceramic nanostructures, the solution injection rate can influence the morphology without, however, supply the real ceramic production rate. In this work, complex superconducting YBa2Cu3O7-x wires were prepared by using the SBS technique. We also show that the morphology can be controlled by varying the injection rate of the polymer solution and the production rate is 4.7 to 33 times higher than the rates of equivalent ceramics produced by ES. Additionally, we also suggest the term Ceramic Production Rate to refer to the production rate of ceramic structures.

Abstract.The manipulation and control of vortex states in superconducting systems are of great interest in view of possible applications, for which mesoscopic materials are good candidates. In this work, we studied the annihilation dynamics and the dissipative aspects of an Abrikosov's vortex-antivortex pair in a mesoscopic superconducting system with a concentric hole. The generalized time-dependent Ginzburg-Landau equations were numerically solved. The main result is the appearance of a phase slip-like line due to the elongation of the vortex and antivortex cores. Under specific circumstances, thermal dissipation might be associated with a sizeable relaxation of the order parameter, so that the energy released in the annihilation of a vortex-antivortex pair might become detectable in measurements of the magnetization as a function of time.

In the present work we report the existence of a crossover between the macroscopic and mesoscopic regimes of vortex interactions in type-II superconductors. Our findings rely on a systematic procedure to determine this crossover, which is based on the influence of the surface on the vortex structure of small superconductors. An adjacent result that we have found is that near this regime transformation, the vortex lattice develops a progressive change of symmetry, from square to hexagonal, which is intimately related to the meso-to-macro crossover. Our numerical simulations have been done for a long superconducting cylinder of square cross section for a wide range of length scales and temperatures.

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We studied the resistive state of a mesoscopic superconducting strip (bridge) at zero external applied magnetic field under a transport electric current, J a , subjected to different types of boundary conditions. The current is applied through a metallic contact (electrode) and the boundary conditions are simulated via the deGennes extrapolation length b. It will be shown that the characteristic current-voltage curve follows a scaling law for different values of b. We also show that the value of J a at which the first vortexantivortex (V-Av) pair penetrates the sample, as well as their average velocities and dynamics, strongly depend on the b values. Our investigation was carried out by solving the two-dimensional generalized time dependent Ginzburg-Landau (GTDGL) equation.

In this work we solved the time-dependent Ginzburg-Landau equations, TDGL, to simulate two superconducting systems with different lateral sizes and with an antidot inserted in the center. Then, by cycling the external magnetic field, the creation and annihilation dynamics of a vortex-antivortex pair was studied as well as the range of temperatures for which such processes could occur. We verified that in the annihilation process both vortex and antivortex acquire an elongated format while an accelerated motion takes place.