Structural and transport measurements for quasimultilayers of Ir-doped YBa2Cu3O7−δ prepared by pulsed-laser deposition are presented. Due to metallic Ir doping, BaIrO3 particles form during film growth. These nanosized particles, having a perovskite structure, grow epitaxially in cube-on-cube relationship inside the film. A strong increase in pinning force density and, hence, Jc was found.

$\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Co}}_x\right)}_2{\text{As}}_2$ superconducting thin films have been grown on ${\text{SrTiO}}_3$ , $\left(\text{La},\text{Sr}\right)\left(\text{Al},\text{Ta}\right){\text{O}}_3$ , ${\text{LaAlO}}_3$ , and ${\text{YAlO}}_3$ (YAO) single crystal substrates by pulsed laser deposition. All the films, except on YAO, have been grown epitaxially without buffer layers. The films deposited on YAO contained 45° in-plane rotated grains and showed a broad superconducting transition. The onset $T_{\text{c}}$ of the films is observed to increase from 16.2 to 24.5 K with increasing $c/a$ , mainly due to a slight distortion of the ${\text{AsFe}}_4$ tetrahedron. From this correlation, we expect that higher superconducting transition temperatures than 24.5 K in a strained epitaxial film may be possible.

The addition of mixed double perovskite Ba₂Y(Nb/Ta)O₆(BYNTO) to YBa₂Cu₃O_7−δ(YBCO) thin films leads to a large improvement of the in-field current carrying capability. For low deposition rates, BYNTO grows as well-oriented, densely distributed nanocolumns. We achieved a pinning force density of 25 GN/m³at 77 K at a matching field of 2.3 T, which is among the highest values reported for YBCO. The anisotropy of the critical current density shows a complex behavior whereby additional maxima are developed at field dependent angles. This is caused by a matching effect of the magnetic fieldsc-axis component. The exponentNof the current-voltage characteristics (inversely proportional to the creep rateS) allows the depinning mechanism to be determined. It changes from a double-kink excitation below the matching field to pinning-potential-determined creep above it.

The biaxially textured growth of superconducting Co-doped BaFe2As2 (Ba-122) thin films has been realized on ion beam assisted deposition (IBAD) MgO coated conductor templates by employing an iron buffer architecture. The iron pnictide coated conductor showed a superconducting transition temperature of 21.5 K, which is slightly lower than that of Co-doped Ba-122 films on single crystalline MgO substrates. A self-field critical current density of over 10^5 A/cm2 has already been achieved even at 8 K. The current experiment highlights the potential of possible coated conductor applications of the iron-based superconductors.Comment: 4 pages, 5 figures. To be published in Applied Physics Expres

${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7/{\mathrm{Y}\mathrm{S}\mathrm{Z}/\mathrm{C}\mathrm{e}\mathrm{O}}_2$ heterostructures have been grown epitaxially on biaxially textured Ni substrates by pulsed laser deposition. The texture of the film was determined by electron backscattering diffraction, providing information on the propagation of the grain boundary network from the Ni substrate to the ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ film via the epitaxial growth. The grain boundary network limits the critical current density to 0.3 ${\mathrm{M}\mathrm{A}/\mathrm{c}\mathrm{m}}^2$ (77 K, 0 T), compared with 1.3 ${\mathrm{M}\mathrm{A}/\mathrm{c}\mathrm{m}}^2$ (77 K, 0 T) for a film grown on a single crystalline Ni substrate. Transport measurements on the coated conductor sample at different temperatures and magnetic fields show that there is a crossover field between intergrain and intragrain critical current that is shifted to higher magnetic fields as the temperature is reduced.

The discovery of superconductivity with a transition temperature, T_c, up to 65 K in single-layer FeSe (bulk T_c=8 K) films grown on SrTiO₃ substrates has attracted special attention to Fe-based thin films. The high T_c is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of superconductivity in the parent compound BaFe₂As₂ (no bulk T_c) just by tensile lattice strain without charge doping. We investigate the interplay between strain and superconductivity in epitaxial BaFe₂As₂ thin films on Fe-buffered MgAl₂O₄ single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe–Fe distance due to the lattice misfit, which leads to a suppression of the antiferromagnetic spin density wave and induces superconductivity with bulk T_c≈10 K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors.