Nanosized Pinning Centers in the Rare Earth-Barium-Copper-Oxide Thin-Film Superconductors

Optimization of high-temperature superconducting bilayer structures using a vortex dynamics simulation

We argue that the current carrying properties of high-temperature superconducting thin films can be further improved, in particular under the mid-field range (B ≈ 0.1-2 T), via introduction of multilayer structures that compromise between good zero field critical current and vortex pinning performance. In this work we focus on a simple bilayer structure consisting of two adjacent layers of pure YBa₂Cu₃O6+x(YBCO) and BaZrO₃(BZO) doped YBCO under magnetic field within the mid-field range oriented parallel to thec-axis of the YBCO unit cell. We have utilized a computational model to simulate the vortex dynamics limited critical current separately from the associated zero field current, which is addressed analytically. The obtained results have allowed us to estimate the optimal layer thicknesses as a function of magnetic field. Our idealized model suggests that the thickness of the doped layer should be substantially smaller than the undoped one, that is around 30% of the total thickness of the film. We have estimated that the current carrying capability of the optimized bilayer structure can be up to 50% higher when compared with corresponding single layer films. Possible deviations from the obtained results associated with the idealized model, most prominently the effect of natural defects, are comprehensively discussed. Our results provide the foundation for the future experimental realization of the proposed bilayer structures. The comparison between the presented results and experimental realization would enable further study of the underlying primitive vortex interactions.

The Application of X-ray Micro-CT in the Study of HTS Tape Coils

In the process of manufacturing products from high-temperature superconductors (HTS), quality control must be carried out. Traditionally, for HTS coils, electrical tests are carried out to determine critical current. In the case of an unacceptable result, it is necessary to determine the cause. Therefore, it is necessary to develop nondestructive testing methods. This article proposes a technology for manufacturing quality evaluation. It is based on determining the actual location of the tape and the gaps between the turns and rows of the coil and analyzing these values. For this purpose, samples were scanned using computed tomography (CT) with a Nordson Dage XD7600NT X-ray inspection system with a μCT module. The obtained data were analyzed using VolumeGraphics VGStudio 2.2 software. Furthermore, the proposed technology can be used as part of a predictive analysis of the state of HTS coils in the windings of electrical machines.

The universal relationship between sample dimensions and cooperative phenomena: effects of fractal dimension on the electronic properties of high-TC cuprate observed using electron spin resonance

As demonstrated by the unique electronic properties of nanostructured materials, which are qualitatively different from the bulk properties of the same materials, there should be a general relationship between the dimensions of the sample structures and the physical/chemical properties. However, it is demanding to examine this intriguing problem experimentally, because one cannot prepare a series of samples based on the same material with systematically varying and noninteger dimensions. This problem is solved by considering the fractal dimensions of samples. The electronic structures of a series of powder samples of the high-T_C superconductor YBa₂Cu₃O_7-δ with the fractal dimensions (D_f) of 2.5-3.0 were investigated using the electron spin resonance (ESR) spectra at 293 K, to determine a general and quantitative relationship between the electronic properties and fractal dimensions of the samples. The observed D_f-dependences of ESR parameters, such as g-values and linewidths, were quantitatively consistent with those of the critical temperatures, critical current densities, and lower critical magnetic fields, all of which exhibited anomalies at D_f ∼ 2.9. Considering the geometrical features of the fractal models, a hypothesis for explaining the observed D_f-dependences of the cooperative phenomena has been proposed, suggesting a universal structural instability at particular fractal dimensions, which affects all the physical and chemical properties of the samples.

Supercurrent Induced by Chiral Coupling in Multiferroic/Superconductor Nanostructures

We study the transport and the superconducting dynamics in a layer of type II superconductor (SC) with a normal top layer that hosts a helical magnetic ordering that gives rise to spin-current-driven ferroelectric polarization. Proximity effects akin to this heterostructure result in an anisotropic supercurrent transport and modify the dynamic properties of vortices in the SC. The vortices can be acted upon and controlled by electric gating or other means that couple to the spin ordering in the top layer, which, in turn, alter the superconducting/helical magnet coupling characteristics. We demonstrate, using the time dependent Ginzburg-Landau approach, how the spin helicity of the top layer can be utilized for pinning and guiding the vortices in the superconducting layer.