2026-01-08 東北大学
図1. (a) PT対称磁性体の電子状態（フェルミ面）の概念図。電流印加によりフェルミ面がシフトし、系全体で面内方向に歪んだ電子ネマティック液晶状態が実現する。(b) SrMnBi2の結晶構造の模式図（左）。四面体に囲まれたMnサイトがPT対称反強磁性秩序を示す。二次元Bi層のディラック電子が形成する電子ポケットの概念図（右）。層間方向の電流により、面内で等方的な4回対称から異方的な2回対称（ネマティック状態）となる。
＜関連情報＞
- https://www.tohoku.ac.jp/japanese/2026/01/press20260108-01-Dirac.html
- https://www.tohoku.ac.jp/japanese/newimg/pressimg/tohokuuniv-press20260108_01web_Dirac.pdf
- https://www.nature.com/articles/s41467-025-67229-y
パリティ時間対称反強磁性体における電流誘起ネマティックディラックバレーの輸送証拠 Transport evidence of current-induced nematic Dirac valleys in a parity-time-symmetric antiferromagnet
Hideaki Sakai,Yuya Miyamoto,Motoi Kimata,Hikaru Watanabe,Yoichi Yanase,Masayuki Ochi,Masaki Kondo,Hiroshi Murakawa & Noriaki Hanasaki
Nature Communications Published:07 January 2026
DOI:https://doi.org/10.1038/s41467-025-67229-y
Abstract
Itinerant antiferromagnets with broken time-reversal symmetry have recently attracted attention, since their spin-split bands enable large magnetotransport responses comparable to ferromagnets despite the negligible spontaneous magnetisation. When the inversion symmetry is further broken by the antiferromagnetic order, the emerging odd-parity multipole order renders the bands spin-degenerate but asymmetric in the momentum space. For such parity-time-symmetric antiferromagnets, it has been predicted that electronic nematicity is induced by current, allowing unconventional nonlinear transport phenomena. However, their experimental evidence has been lacking. Here, we report two-fold nonreciprocal angular magnetoresistance in the tetragonal layered Dirac material SrMnBi2 with parity-time-symmetric antiferromagnetic order in its Mn-Bi layers. By quantitatively modelling the angular and field dependencies using a phenomenological framework, we reveal that the observed nonreciprocal interlayer resistivity arises from the current-induced breaking of four-fold rotoinversion symmetry of the Dirac valleys in the Bi square net adjacent to the Mn-Bi layer. Furthermore, we demonstrate the alignment of parity-time-symmetric antiferromagnetic domains via current-field cooling, achieving electric-magnetic control of the f-wave polarity in momentum space. The observed switchable nonreciprocal transport associated with current-tuneable valley nematicity paves the way for novel antiferromagnetic spintronic and valleytronic applications.
