Skyrmions and spin moiré superlattices in triangular-lattice magnets

Frustrated magnets, characterized by competing interactions that suppress conventional magnetic order, can host unconventional spin textures with emergent electromagnetic responses. Magnetic skyrmions, topologically nontrivial spin solitons, are often found in noncentrosymmetric materials or interfacial symmetry-broken heterostructures. However, theories predict that magnetic frustration can also stabilize skyrmions. We have experimentally demonstrated and established a design principle for centrosymmetric skyrmion-hosting materials. Using resonant x-ray scattering and transport measurements, we have identified a skyrmion-lattice state in centrosymmetric Gd-based materials, including the triangular-lattice magnet Gd₂PdSi₃ [1]. These systems exhibit emergent electromagnetic properties, such as a giant topological Hall effect arising from the enhanced emergent magnetic field of the nanometric skyrmions.

In addition, we explore rare-earth-based layered semimetals with spin moiré superlattices, where multiple incommensurate spin modulations are superimposed to generate a periodic exchange potential, as in the crystallographic moiré superlattices due to twist or lattice mismatch. We observed the field-induced transitions to multiple-q spin moiré states accompanied by significant resistivity changes and giant Hall response in EuAg₄Sb₂ [2]. Electronic structure studies using ARPES, quantum oscillations, and DFT calculations reveal a quasi two-dimensional Fermi surface nested to a magnetic Brillouin zone of the spin moiré superlattice. The long mean free path of the conduction electrons, exceeding the period of the spin modulation, enables the realization of the reconstructed Fermi surfaces and the anomalous transport behavior.

Time permitting, I will talk about the recent exploration of new rare earth intermetallics that exhibit unconventional magnetic structures and anomalous magnetotransport properties [3,4].