We performed high-resolution angle-resolved photoemission spectroscopy on electron-doped high-$T_c$ superconductor ${\mathrm{Pr}}_{0.89}{\mathrm{LaCe}}_{0.11}{\mathrm{CuO}}_4$ to study the anisotropy of the superconducting gap. The observed momentum dependence is basically consistent with the $d_{x^2-y^2}$-wave symmetry, but obviously deviates from the monotonic $d_{x^2-y^2}$ gap function. The maximum gap is observed not at the zone boundary, but at the hot spot where the antiferromagnetic spin fluctuation strongly couples to the electrons on the Fermi surface. The present experimental results suggest the spin-mediated pairing mechanism in electron-doped high-$T_c$ superconductors.

The doping dependence of electronic states in an electron-doped high-temperature superconductor (HTSC) ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x\mathrm{Cu}{\mathrm{O}}_4$ was studied by high-resolution angle-resolved photoemission spectroscopy. We observed that the high-energy pseudogap around the hot spot shows an abrupt filling-in at the magnet-superconductor phase boundary, resulting in the unusual reconstruction of the Fermi surface. The magnitude $\left({\Delta }_{\mathrm{PG}}\right)$ and the temperature $\left(T^{*}\right)$ at which the pseudogap is filled-in show a close relation to the effective hyperfine coupling energy $\left(J_{\mathrm{eff}}\right)$ and the spin-correlation length $\left({\xi }_{\mathrm{AF}}\right)$, respectively. These results suggest the magnetic origin of the pseudogap and the unconventional nature of the magnet-superconductor phase transition in electron-doped HTSC.

The electronic structure of single crystals ${\mathrm{Na}}_{0.6}{\mathrm{CoO}}_2$, which are closely related to the superconducting ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_2·y{\mathrm{H}}_2\mathrm{O}$ ($T_c\sim 5\mathrm{K}$), is studied by angle-resolved photoelectron spectroscopy. While the measured Fermi surface (FS) is consistent with the large FS enclosing the $\Gamma$ point from the band theory, the predicted small FS pockets near the $K$ points are absent. In addition, the band dispersion is found to be highly renormalized, and anisotropic along the two principal axes ($\Gamma \mathrm{\text{−}}K$, $\Gamma \mathrm{\text{−}}M$). Our measurements also indicate that an extended flatband is formed slightly above $E_F$ along $\Gamma \mathrm{\text{−}}K$.

Numerical simulations of the geodynamo have successfully represented many observable characteristics of the geomagnetic field, yielding insight into the fundamental processes that generate magnetic fields in the Earth's core. Because of limited spatial resolution, however, the diffusivities in numerical dynamo models are much larger than those in the Earth's core, and consequently, questions remain about how realistic these models are. The typical strategy used to address this issue has been to continue to increase the resolution of these quasi-laminar models with increasing computational resources, thus pushing them toward more realistic parameter regimes. We assess which methods are most promising for the next generation of supercomputers, which will offer access to O(10⁶) processor cores for large problems. Here we report performance and accuracy benchmarks from 15 dynamo codes that employ a range of numerical and parallelization methods. Computational performance is assessed on the basis of weak and strong scaling behavior up to 16,384 processor cores. Extrapolations of our weak-scaling results indicate that dynamo codes that employ two-dimensional or three-dimensional domain decompositions can perform efficiently on up to ∼10⁶ processor cores, paving the way for more realistic simulations in the next model generation.

We performed high-resolution angle-resolved photoemission spectroscopy on ${\mathrm{N}\mathrm{d}}_{1.87}{\mathrm{C}\mathrm{e}}_{0.13}{\mathrm{C}\mathrm{u}\mathrm{O}}_4$, which is located at the boundary of the antiferromagnetic (AF) and the superconducting phase. We observed that the quasiparticle (QP) effective mass around $(\pi ,0)$ is strongly enhanced due to the opening of the AF gap. The QP mass and the AF gap are found to be anisotropic, with the largest value near the intersecting point of the Fermi surface and the AF zone boundary. In addition, we observed that the QP peak disappears around the Néel temperature ($T_N$) while the AF pseudogap is gradually filled up at much higher temperatures, possibly due to the short-range AF correlation.