Novel Antiferromagnetic Topological Insulator NdBi Studied by Micro-ARPES*

Antiferromagnetic topological insulators (AF TI) are known to host a massive Dirac cone (DC) surface state despite the absence of net magnetic moment. Moreover, a massless feature of DC shows a significant dependence on the orientation of the Néel vector. In order to clarify such DC characteristics associated with the AF-TI nature, we performed angle-resolved photoemission spectroscopy (ARPES) to directly visualize the DC states of AF TI.

Here, we focus on the rare-earth monopnictide NdBi, which shows semimetallic properties, topologically non-trivial nature, and AF transition at low temperature. To overcome the experimental difficulty in resolving ARPES signal from multiple AF domains at the cleaved surface, we have developed a micro-ARPES system with a spot size of 12 × 10 µm² at Photon Factory, KEK, and performed domain selective ARPES measurements on NdBi. As a result, we have succeeded in directly observing massive and massless DC states on the cleaved surface. Furthermore, we have identified the relationship between the AF domains and the DC states by clarifying the rotational symmetry of the surface at each AF domain. We discuss the origin of this DC behavior in terms of the observed symmetry pattern in ARPES spectra and crystal symmetry in the AF state.