A research team led by the Ningbo Institute of Materials Technology and Engineering (NIMTE), CAS, has achieved a breakthrough in spintronics by demonstrating that nonsymmorphic symmetry in hexagonal SrIrO₃ protects topological Dirac semimetal states. This unique electronic structure leads to record-breaking charge-spin conversion efficiency, enabling magnetic switching with ultra-low power dissipation. The study establishes a robust and universal criterion for designing future energy-efficient spintronic devices.

As is well known, the Earth behaves like a “giant magnet” (that is, it possesses a dipole magnetic field*1), and this magnetic field is thought to be generated by a dynamo process*2 driven by thermal convection of liquid iron in the Earth’s outer core. Paleomagnetism studies have shown that the Earth’s magnetic field reverses its polarity at irregular intervals, ranging from several hundred thousand to about ten million years. However, the physical mechanism responsible for these reversals remains unresolved. In particular, it is still not well understood how the polarity of the magnetic field - northward or southward - is determined.

Focusing on this polarity-determination mechanism, a research team at the National Institute for Fusion Science (NIFS) and the Graduate University for Advanced Studies, SOKENDAI, carried out a detailed study of a convective dynamo arising in a spherical-shell plasma having the same geometry as the Earth’s outer core, using three-dimensional magnetohydrodynamic simulations*3. As a result, they showed for the first time that, in an Earth-like dynamo, the polarity of the magnetic field (northward or southward) is determined randomly, not by the direction of convection, but by extremely weak magnetic perturbations present initially. Moreover, depending on subtle differences in the imposed magnetic perturbations, the system settles into either a northward - or southward- polarity state and remains there (bi-stability of the dipole polarity). Thus, the polarity of the Earth’s magnetic field may likewise have been determined by tiny fluctuations present when the geodynamo first emerged some four billion years ago. That polarity would then be expected to persist, yet in reality the geomagnetic field undergoes repeated reversals. This suggests that geomagnetic reversals may be caused by physical effects not included in the present computational model.

Endowing and controlling topologically structured emission in microlasers is highly desired yet remains challenging. Toward this goal, researchers at Fudan University developed a compound topological microcavity design for vectorial lasing with designable topological charges. Leveraging quasi-BIC Möbius-like correspondence, they establish a direct, predictive link between cavity morphology and topological charge of emitted lasing profile. Experimentally, they demonstrate vectorial lasing with topological charges from −5 to +5, representing a substantial advance toward compact topological light sources.