We studied the flux pinning properties of BaZrO 3 -doped YBa 2 Cu 3 O 7−x and BaSnO 3 -doped YBa 2 Cu 3 O 7−x films. We found that BaSnO 3 -doped films showed very high global pinning forces, F p , of 28.3 GN m −3 (77 K, B c) and 103 GN m −3 (65 K, B c), twice that of BaZrO 3 -doped films. Transmission electron microscopy analysis showed that, in both films, nanorods of the dopant phase were incorporated. The BaSnO 3 nanorods were nearly straight but the BaZrO 3 nanorods became curved with the increasing film thickness.

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BaZrO3 nanorods are known to be effective pinning centers as c-axis-correlated pinning centers. Furthermore, BaZrO3 nanorods in REBa2Cu3Oy (RE: rare-earth element) films are formed by self-assembled stacking of BaZrO3 using a target mixture of a superconductor and BaZrO3 for pulsed-laser deposition, which is a very easy fabrication technique. The density of BaZrO3 nanorods in YBa2Cu3Oy (YBCO) films can be controlled by varying the BaZrO3 content in a target. The BaZrO3 addition has two functions for superconductivity; one is the improvement of pinning forces due to the addition of pinning centers and the other is Tc degradation. The optimum BaZrO3 addition for Jc improvement in magnetic fields is found to be around 3 wt% because of a trade-off between the two functions described above. Furthermore, the length of BaZrO3 nanorods is found to be controlled using two types of target: pure YBCO and a mixture of YBCO and BaZrO3. Varying the BaZrO3 nanorod length has an effect on the pinning mechanism. In particular, magnetic field angle dependences of Jc are varied from c-axis-correlated pinning to nearly random pinning by changing the nanorod length. The magnetic field at the crossover of the pinning mechanism seems to be adjusted by the BaZrO3 nanorod length.

High-temperature superconductors can carry high non dissipative currents at low temperatures as long as quantized vortices are pinned. However, the currents in a magnetic field at liquid nitrogen temperature (77 K) are not sufficiently high for practical use due to the weak pinning. For the improvement of nondissipative currents in YBa2Cu3O7-δ films, linear defects that extended to the c-axis of the film were introduced using a novel nanostructure technology. We observed a marked enhancement of the nondissipative currents even at 77 K and high fields when the fields were applied close to the c-axis. This is a clear demonstration of enhanced pinning using artificially incorporated pinning centers.

YBa2Cu3O7−x+Y2O3-stabilized ZrO2 (YBCO+YSZ) mixed films were prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin YSZ sector on top. The Jc at 77 K for the mixed YBCO+YSZ thin film was enhanced. The Jc at 77 K for the pure film and the mixed YBCO+YSZ thin film were 1.46 and 1.95 MA cm−2 (self field) (and 0.09 and 0.28 MA cm−2 (, B = 5 T)), respectively, even when both films were prepared using the same deposition conditions. The maximum pinning force of a doped film (77 K, ) was 15.9 GN m−3, which is comparable to the value reached by NbTi at 4.2 K. In the YSZ-added sample, the angular dependence of Jc showed a broad peak at due to the flux pinning by the c-axis correlated defects. Elongated nanorods grown parallel to the c axis were consistently observed in the cross-sectional TEM images.

Epitaxial Fe–Te–Se thin films were deposited by pulsed laser deposition at 250–600 °C on SrTiO3 (100), MgO (100), LaAlO3 (100) and CaF2 (100) single crystal substrates. The best superconducting film was grown on CaF2:  K and  K with Tdep = 300 °C and 3 Hz. Critical current density Jc (T = 4.2 K) was 0.41 × 106 A cm−2 at 0 T and 0.23 × 106 A cm−2 at 9 T. The angular dependence of Jc shows a broad c-axis correlated peak when B ≥ 3 T.

YBa 2 Cu 3 O 7−x + BaSnO 3 (YBCO + BSO) mixed films with increasing BSO content were prepared on SrTiO 3 substrates by pulsed laser deposition from YBCO + x wt% BSO mixed targets (x = 2, 3, 4, 5, 6, 8 and 9 wt%). Transmission electron microscopy (TEM) images reveal that BSO is incorporated into the YBCO matrix in form of nanorods, whose density and size increase with increasing BSO content. The pinning properties for the mixed YBCO + BSO film were systematically studied. The 4 wt% sample presents the maximum global pinning forces F P at all considered temperatures: 28.3 GN m −3 near 2 T at 77 K, 103 GN m −3 near 5 T at 65 K, and >241 GN m −3 near 9 T at 40 K.

We introduced high density columnar defects, as artificial pinning centres (APCs) for quantized vortices, into YBa 2 Cu 3 O 7−x (YBCO) films during the film deposition procedure. APCs were introduced perpendicular to the film surface using nanosized Y 2 O 3 islands prepared on SrTiO 3 (100) substrates by pulsed laser deposition. Varying the deposition parameters and the substrate annealing conditions allowed strong changes in the shape and density of the Y 2 O 3 islands to be induced. The best performance among the APC samples as compared to the pure YBCO film was obtained for that grown on the Y 2 O 3 -deposited substrate with five laser pulses, corresponding to 0.2 Y 2 O 3 monolayers (ML). Even when the 0.2 ML APC films were prepared using the same deposition conditions, the columnar defects enhanced J c at 77 K from 1.8 to 2.7 MA cm −2 (self-field) and from 0.06 to 0.10 MA cm −2 (H = 5 T).