Striving to improve the critical current density Jc of superconducting YBa2Cu3O6+x (YBCO) thin films via enhanced vortex pinning, the interplay between film growth mechanisms and the formation of nanosized defects, both natural and artificial, is systematically studied in undoped and BaZrO3 (BZO)-doped YBCO thin films. The films were grown via pulsed laser deposition (PLD), varying the crystal grain size of the targets in addition to the dopant content. The microstructure of the PLD target has been observed to have a great impact on that of the deposited thin films, including the formation of vortex pinning centers, which has direct implications on the superconducting performance, especially on the isotropy of flux pinning properties. Based on experimentally measured angular dependencies of Jc, coupled with a molecular dynamics (MD) simulation of flux pinning in the YBCO films, we present a quantitative model of how the splay and fragmentation of BZO nanorods artifically introduced into the YBCO film matrix explain the majority of the observed critical current anisotropy.

In order to understand how the doping with self-assembled nanorods of different sizes and concentrations as well as applied magnetic fields affect the critical current anisotropy in YBa 2 cu 3 o 7−x (YBCO) thin films close to YBCO c-axis, we present an extensive and systematic computational study done by molecular dynamics simulation. the simulations are also used to understand experimentally measured J c (θ) curves for BaHfO 3 , BaZrO 3 and BaSno 3 doped YBCO thin films with the help of nanorod parameters obtained from transmission electron microscopy measurements. our simulations reveal that the relation between applied and matching field plays a crucial role in the formation of J c (θ)-peak around YBCO c-axis (c-peak) due to vortex-vortex interactions. We also find how different concentrations of different size nanorods effect the shape of the c-peak and explain how different features, such as double c-peak structures, arise. In addition to this, we have quantitatively explained that, even in an ideal superconductor, the overdoping of nanorods results in decrease of the critical current. our results can be widely used to understand and predict the critical current anisotropy of YBco thin films to improve and develop new pinscapes for various transport applications.High temperature superconductors (HTS) are expected to have large number of applications in different fields of technology and power industry in the future 1-3 . Since all known HTS are of type II, the critical current passed through them is highly dependent on the surrounding magnetic field due to the movement of vortices. Thus, to enhance and widen the usability of HTS, the dynamics of vortices need to be well understood.Among the high temperature superconductors, YBa 2 Cu 3 O 7−x (YBCO) seems the most practical choice when thinking for the applications 1 . The intrinsic anisotropy of the critical current, in thin films and coated conductors, can be modified by adding impurities within the lattice of YBCO which pin the vortices restricting their movement. Based on growth conditions and lattice mismatch between the YBCO and the dopant as well as their elastic properties 4,5 , impurities such as Y 2 O 3 6 , BaCeO 3 7-9 and BaZrO 3 (BZO) 10,11 can form uncorrelated randomly distributed nanoparticles within the YBCO lattice. Under optimized deposition conditions, via a spontaneous phase-separation and strain-driven self-assembly process during film deposition 12 , self-assembly of nanorods of BaHfO 3 (BHO) 1 , BaZrO 3 (BZO) 4,13,14 , BaSnO 3 (BSO) 15,16 , Ba 2 YTaO 3 (BYTO) 17 or Ba 2 YNbO 6 (BYNO) 18 within the YBCO lattice can be realized.Recently, a topic of interest has been to add both point-like nanodots and nanorods within the YBCO lattice simultaneously. This has been achieved by doping YBCO simultaneously with both BYTO and BYNO (referred as BYNTO) with an additional rare earth oxide, leading to continuous niobiate/tantalate nanorods and rare-earth oxide nanoparticles 19 . A lot of experimental research has been done in order to understand the...

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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 the c-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.

To maximize the flux pinning in high-temperature superconductor (HTS) thin film applications, we have experimentally studied the effect of BaZrO 3 (BZO) nanorod den- sity within the YBa 2 Cu 3 O 6+x (YBCO) lattice. Even though the BZO decreases the self-field critical current density J c (0) and the absolute J c (B) at high fields is observed being the highest for 4 % BZO doped YBCO, the maximized pinning property is ob- served at the level of 10 % of BZO, when the distance between the outer edge of the nanorods is in the order of the diameter of the nanorod. In general, as also theoretically calculated, the flux pinning is increased even above 10 % of BZO, but the improvement is limited by disturbance of the nanorod growth, weakening the flux pinning and de- creasing the absolute J c drastically. The results evidently show that by maximizing the flux pinning using higher BZO doping concentration than earlier expected and tak- ing care of the maximum self-field J c (0) , which is strongly dependent on the electron mean free path, would offer the keys to resolve the challenges in the future HTS power applications.