Enhanced flux pinning isotropy by tuned nanosized defect network in superconducting YBa2Cu3O6+x films

Nd:YAG infrared laser as a viable alternative to excimer laser: YBCO case study

We report on the growth and characterization of epitaxial YBa[Formula: see text]Cu[Formula: see text]O[Formula: see text] (YBCO) complex oxide thin films and related heterostructures exclusively by Pulsed Laser Deposition (PLD) and using first harmonic Nd:Y[Formula: see text]Al[Formula: see text]O[Formula: see text] (Nd:YAG) pulsed laser source ([Formula: see text] = 1064  nm). High-quality epitaxial YBCO thin film heterostructures display superconducting properties with transition temperature [Formula: see text] 80 K. Compared with the excimer lasers, when using Nd:YAG lasers, the optimal growth conditions are achieved at a large target-to-substrate distance d. These results clearly demonstrate the potential use of the first harmonic Nd:YAG laser source as an alternative to the excimer lasers for the PLD thin film community. Its compactness as well as the absence of any safety issues related to poisonous gas represent a major breakthrough in the deposition of complex multi-element compounds in form of thin films.

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.

Vortex dynamics simulation for pinning structure optimization in the applications of high-temperature superconductors

We introduce a molecular dynamics based simulation model that enables the efficient optimization of complex pinning structures in unpresented wide magnetic field and angular ranges for high-temperature superconductor applications. The fully three-dimensional simulation allows the modeling of the critical current and the associated anisotropy in the presence of any kinds of defects despite their size and orientation. Most prominently, these include artificial defects such as nanorods along with intrinsic weak-links orab-plane oriented stacking faults, for example. In this work, we present and analyze the most fundamental results of the simulation model and compare them indirectly with a wide range of previous experimental and computational observations. With the provided validation for the proposed simulation model, we consider it to be an extremely useful tool in particular for pushing the limits of ampacity in the coated conductor industry.

Contactless Mechanical Power Transmission Through the High-T c Superconducting Pinning Effect

Mechanical power transmission (MPT) components are almost indispensable for every engineering equipment with motions. In order to satisfy some rigorous requirements, such as contamination free and zero leakage in the mixing process of biomedical solutions, a contactless MPT mode was proposed in this study based on the high-T _c superconducting flux pinning mechanism. It makes the stirring container with the driven part inside that can be totally isolated from the external environment. The physical principle of superconducting flux pinning effect was discussed firstly to explore a feasible structural scheme, which can completely restrain all the six degrees of freedom (DOFs) by the linkage of magnetic flux lines. Then, a measurement device was established to verify and investigate the proposed contactless MPT mode. The motion can be transferred synchronously from the superconducting driving part to the permanent magnet driven part since they are unified as an integrity through the pinned flux lines. The influence of driving speed, cooling clearance, and magnet arrangement on the transmitted torque was analyzed. The verified contactless MPT mode also has the advantages of self-stability and overload protection, which can avoid the drawbacks of traditional permanent magnetic transmission mode.

Control of the nanosized defect network in superconducting thin films by target grain size

A nanograined YBCO target, where a great number of grain boundaries, pores etc. exist, is shown to hold an alternative approach to future pulsed laser deposition based high-temperature superconductor thin film and coated conductor technologies. Although the nanograined material is introduced earlier, in this work, we comprehensively demonstrate the modified ablation process, together with unconventional nucleation and growth mechanisms that produces dramatically enhanced flux pinning properties. The results can be generalized to other complex magnetic oxides, where an increased number of defects are needed for modifying their magnetic and electrical properties, thus improving their usability in the future technological challenges.

Electrical conduction mechanisms of metal / high-T c superconductor (YBCO) interfaces

Current-voltage characteristics of Au/YBa₂Cu₃O[Formula: see text] interfaces (Au/YBCO), built on optimally-doped YBCO thin films, grown by pulsed laser deposition, were measured as a function of temperature in the 50 K to 270 K range, for two different resistance states. A non-trivial equivalent circuit model is proposed, which reveals the existence of a highly inhomogeneous scenario composed by two complex layers: one presenting both a non-linear Poole-Frenkel conduction as well as variable range hopping localization effects (probably associated with YBa₂Cu₃O₆) mixed with a minor metallic phase, while the other is also composed by a mixture of YBCO with different oxygen contents, where a metallic ohmic phase still percolates. A microscopic description of the effects produced by the resistance switching is given, showing the evolution of carrier traps, localization effects and dielectric behavior for each state. The dielectric behavior is interpreted in terms of a Maxwell-Wagner scenario.

Superconducting HfO2-YBa2Cu3O7−δ Nanocomposite Films Deposited Using Ink-Jet Printing of Colloidal Solutions

To reduce the fabrication costs while maximizing the superconducting and pinning properties of YBa2Cu3O7−δ (YBCO) nanocomposite films, the drop-on-demand ink-jet printing technique was used to deposit colloidal YBCO inks onto LaAlO3 substrates. These inks containing preformed HfO2 nanocrystals were carefully adjusted, prior to the jettability, as the droplet formation depends on the rheological properties of the inks themselves. After carefully adjusting printing parameters, 450-nm thick pristine YBCO films with a self-field critical current density (Jc) of 2.7 MA cm−² at 77 K and 500-nm thick HfO2-YBCO nanocomposite films with a self-field Jc of 3.1 MA·cm−² at 77 K were achieved. The final HfO2-YBCO nanocomposite films contained dispersed BaHfO3 particles in a YBCO matrix due to the Ba2+ reactivity with the HfO2 nanocrystals. These nanocomposite films presented a more gradual decrease of Jc with the increased magnetic field. These nanocomposite films also showed higher pinning force densities than the pristine films. This pinning enhancement was related to the favorable size and distribution of the BaHfO3 particles in the YBCO matrix.