2026-09-17 東京大学,大阪大学
本研究では、磁石の性質を持つ特殊な電子「磁性ディラック電子」を直接観測し、100％スピンが揃った「完全スピン偏極電流」を実現するための電子状態を実証しました。
＜関連情報＞
- https://www.issp.u-tokyo.ac.jp/maincontents/news2.html?pid=32233
- https://www.nature.com/articles/s41467-026-77571-4
反強磁性トポロジカル絶縁体NdBiにおけるスピン偏極表面ディラックギャップの直接観測 Direct observation of a spin-polarized surface Dirac gap in the antiferromagnetic topological insulator NdBi
Yuto Fukushima, Hiroyuki S. Suzuki, Masayuki Ochi, Takuma Nishida, Toshiya Ikenobe, Hiraku Saito, Yuto Kinoshita, Kaishu Kawaguchi, Hiroaki Tanaka, Ayumi Harasawa, Takushi Iimori, Koichiro Yaji, Masashi Tokunaga, Taro Nakajima, Kiyohisa Tanaka, Takahiro Morimoto, Ryo Mori & Takeshi Kondo
Nature Communications Published:15 September 2026
DOI:https://doi.org/10.1038/s41467-026-77571-4 Early Provide
Abstract
A gapped Dirac cone in antiferromagnetic topological insulators (AFM-TIs) is essential for realizing the quantized anomalous Hall effect, yet its intrinsic magnitude remains controversial. In the prototypical AFM-TI MnBi2Te4, however, the observed Dirac gap is significantly smaller than theoretical predictions or nearly absent, highlighting a long-standing discrepancy. Here we demonstrate that NdBi hosts a spin-polarized topological surface Dirac cone with a sizable gap of 17 ± 2 meV at the Dirac point, in excellent agreement with density functional theory predictions (12 meV). This direct observation is enabled by high-resolution 7 eV laser-based spin- and angle-resolved photoemission spectroscopy, which unambiguously disentangles the spin-polarized surface Dirac cone from bulk-derived states. Furthermore, through temperature dependence and controlled surface contamination, we establish a direct linkage between surface magnetism and the Dirac gap, demonstrating that the gap opens only in the presence of surface magnetic order. These results provide definitive spectroscopic evidence for an intrinsic Dirac gap in AFM-TIs and establish NdBi as a model platform to resolve the long-standing discrepancy between experiment and theory in AFM-TIs.
