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Y2O3 nanoparticles prepared by an inert gas phase condensation process were used to introduce artificial pinning centres in YBa2Cu3O7[?]d thin films. The areal density of the particles was varied between 120 and 4200 particles um[?]2 without changing the mean particle diameter of approximately 9 nm. Y2O3 particles were deposited on TiO2 terminated SrTiO3 (100) single-crystal substrates with areal densities up to 1654 particles um[?]2 and subsequently covered with YBa2Cu3O7[?]d by off-axis pulsed laser deposition (PLD). The areal density of the room temperature deposited particles is not changed by the substrate heating during PLD although their height on the substrate decreases. An influence on Jc is demonstrated for particle densities above 1588 particles um[?]2, indicating that the substrate decoration with Y2O3 nanoparticles from the gas phase affects the formation of artificial pinning centres in the YBa2Cu3O7[?]d films and can be applied to further study of the effect of particle size and areal density on defect formation in YBa2Cu3O7[?]d. [ABSTRACT FROM AUTHOR]

Abstract A quantum critical point (QCP) is currently being conjectured for the BaFe2(As1−x P x )2 system at the critical value x c ≈ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such a universal behavior has not, however, been found in the superconducting upper critical field H c2. Here we report H c2 data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that H c2 is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe2(As1−x P x )2. The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.

Power applications based on YBa2Cu3O7[?]d coated conductors demand an enhancement of the critical current density Jc in magnetic fields to be achieved using artificial pinning centres. A well-known approach to studying pinning by second phase nanoparticles is based on quasi-multilayer deposition of YBa2Cu3O7[?]d (Y123) and a dopant material. In this study we use the Y2Ba4CuMOy (M = Nb, Zr; M2411) phase as a dopant material, which proved to be very successful in increasing Jc for bulk samples. Although stability of the M2411 phase in bulk Y123 has been reported, experimental evidence of its stability in thin films is still lacking. We found that during the quasi-multilayer deposition, yttrium doped Ba(M1[?]xYx)O3 forms instead of the M2411 secondary phase, and this causes an increase of Jc at high magnetic fields as well as an increase in the irreversibility field below 80 K as compared against pure Y123 thin films. [ABSTRACT FROM AUTHOR]

In the present work, the single buffer layers of La2Zr2O7 (LZO) with different thicknesses were prepared using pulsed laser deposition (PLD) on highly textured Ni-5 at.%W tapes for YBa2Cu3O7[?]d-coated conductors. The highly textured LZO layers are obtained on the metallic substrates, making the subsequent epitaxial growth of superconducting YBa2Cu3O7[?]d layers feasible. The superconducting transition temperature increases as the LZO thickness increases up to 240 nm, achieving a value of Tc of more than 92 K with a narrow transition width less than 1 K. Inductive measurement reveals that the critical current density (Jc) reaches 0.77 MA cm[?]2 at 77 K in self-field, showing that the single buffer of LZO is comparable to standard buffer architectures such as CeO2/YSZ/Y2O3 or CeO2/LZO. This implies that the LZO as a single buffer layer is promising for the simplification of the preparation process, leading to cost-effective coated conductors. [ABSTRACT FROM AUTHOR]