Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7−δ (YBCO) films with 5 mol% BaZrO3 (BZO) and 5 mol% Y2O3 additions grown on single crystal SrTiO3 substrates by pulsed laser deposition (PLD). The results show that adding BZO+Y2O3 has reduced the thickness dependence of the self-field critical current density (Jcsf), compared to that observed in optimized YBCO films, with a significant enhancement of Jcsf in the thick film region (>2 µm). The so-called ‘dead layer’ did not appear until the film thickness was greater than 6.4  µm. We attribute this improvement to the additional pinning centers introduced in the bulk by the addition and a decrease in microstructure degradation with thickness. As a result, Jcsf remains as high as 2.3 MA cm−2 in a 6.4  µm thick film. The combination of this high Jcsf value and the enhancement of the in-field Jc induced by the additions, which was observed in the whole thickness range, leads to a critical current per centimeter width (Ic−w) in excess of 400 A cm−1 at 1 T and 75.5 K and 530 A cm−1 at 3 T and 65 K under all field directions.

We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa5. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature Tc=18.5  K, which speaks against phonon-mediated superconductivity. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario--evidence for a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing.

We report results of ⁵⁹Co nuclear magnetic resonance measurements on a single crystal of superconducting PuCoGa₅ in its normal state. The nuclear spin-lattice relaxation rates and the Knight shifts as a function of temperature reveal an anisotropy of spin fluctuations with finite wave vector q. By comparison with the isostructural members, we conclude that antiferromagnetic XY-type anisotropy of spin fluctuations plays an important role in mediating superconductivity in these heavy fermion materials.

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