Taichi Okuda

Chiral helimagnets based on intercalated transition-metal dichalcogenides, characterized by nanoscale spin ordering, provide a powerful route to engineer chiral spin textures (e.g., the topologically protected magnetic solitons) and explore emergent electronic functionalities associated with their surface and interface electronic structures. However, despite growing interest, direct experimental studies of termination-dependent surface electronic structures and their temperature-driven magnetic evolution remain largely unexplored, hindering a microscopic understanding of the electronic states that is crucial for the development of low-dimensional spintronic devices. Here, taking Cr1/3TaS2 as a representative example, we systematically investigate the termination-dependent surface electronic states of the chiral helimagnets and uncover their distinct temperature evolution across the magnetic transition (TC ∼ 142 K) by combining high-resolution angle-resolved photoemission spectroscopy with a microfocused beam and surface-state-resolved first-principles calculations. The TaS2-terminated surface hosts folded monolayer-like TaS2 bands under the √3 × √3 superlattice potential and a shallow triangular electron pocket at the superlattice K̅ point arising from Cr–Ta orbital hybridization. In contrast, the Cr-terminated surface exhibits reconstructed hole pockets with pronounced magnetic band splitting. This splitting disappears above TC and closely follows the temperature evolution of the magnetization, providing a direct spectroscopic fingerprint of the underlying magnetic order. In addition, multiple ultranarrow Cr-d-derived surface flat bands are resolved. These findings demonstrate that Cr1/3TaS2 serves as a model system in which surface electronic states are strongly coupled to chiral magnetism, with potential relevance to chiral spintronic and valleytronic micro/nanodevices.

The band structure of ultrathin Pd(111) thin films grown on the Cr₂O₃(0001) surface was studied by angule-resolved photoemission spectroscopy (ARPES) combined with first-principles calculations. The Cr₂O₃(0001) interface and the expanded Pd lattice constant appears to significantly affect the occupied band structure of an ultrathin palladium film. A characteristic band splitting is seen in the experimental occupied electronic structure, forming a hexagonal pattern approximately half-way from the Γ ¯ point to the surface Brillouin zone boundary. The ARPES spectrum near the Fermi level is reproduced by the first-principles simulation for a Pd monolayer (ML) placed on the Cr-terminated Cr₂O₃ surface with the energetically favorable lateral stacking. In this configuration, the Pd bands inside the Cr₂O₃ band gap have a significant, momentum-dependent exchange splitting, which matches with the experimentally observed band splitting. The experimental band structure shows a band with an electron effective mass close to the free electron mass, neglecting mass enhancement effects close to the Fermi level. From the hybridization of the Pd ML with the Cr₂O₃(0001) substrate, a hole band with a mass of −0.48 ± 0.02 is identified.

Spin splitting in electronic band structures via antiferromagnetic orders is a new route to control spin-polarized carriers that is available for spintronics applications. Here, we investigated the spin degrees of freedom in the electronic band structures of the antiferromagnet NdBi using laser-based spin- and angle-resolved photoemission spectroscopy (laser-SARPES). Our laser-SARPES experiments revealed that the two surface bands that appear in the antiferromagnetic state are spin polarized in opposite directions as a counterpart of the spin splitting. Moreover, we observed that the spin polarization is antisymmetric to the time-reversal invariant momentum, indicating that spin degeneracy is lifted due to the breaking of inversion symmetry at the surface. These results are well reproduced by our density functional theory calculations with the single- q magnetic structure, implying that the spin-split surface state is determined by the breaking of inversion symmetry in concert with the antiferromagnetic order.