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The measured electronic structure of Nd${}_{2}$Ir${}_{2}$O${}_{7}$ through its metal-insulator transition indicates an unusual Slater to Mott crossover with reducing temperature. This constrains theoretical models which suggest this material has topologically protected magnetic states.

PrV2Al20 is a rare example of a heavy-fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc=50 mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy-fermion character of the superconductivity is evident from the specific heat jump of ΔC/T∼0.3 J/mol K(2) and the effective mass m*/m0∼140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ=0.75 K and T*=0.65 K associated with quadrupole and octupole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T(3) dependence, indicating the gapless mode associated with the quadrupole order, the octupole order, or both. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.

The dependence of the critical current density ${J}_{c}$ on hydrostatic pressure to 0.6 GPa is determined for a single 25\ifmmode^\circ\else\textdegree\fi{} [001]-tilt grain boundary in a bicrystalline ring of nearly optimally doped melt-textured ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$. ${J}_{c}$ is found to increase rapidly under pressure at $+20%/\mathrm{GPa}$. A new diagnostic method is introduced (pressure-induced ${J}_{c}$ relaxation) which reveals a sizable concentration of vacant oxygen sites in the grain boundary region. Completely filling such sites with oxygen anions should lead to significant enhancements in ${J}_{c}$.