Atomic-scale spin sensing of a 2D d-wave altermagnet via helical tunneling

Altermagnets simultaneously possess momentum-dependent nonrelativistic spin splitting and zero net magnetization (1-6). Their defining crystalline symmetry connects opposite-spin sublattices in real space and imposes alternating spin polarization on the symmetry-related electronic states in momentum space (1-3). Identifying such an order and its associated spin response therefore calls for atomic-scale spin-sensitive measurements in both real and momentum space, an experimental milestone yet to be achieved. Here we show that the helical edge modes of the higher-order topological insulator α-Bi4Br4 can serve as a spin-selective scanning tunnelling microscopy probe of the two-dimensional d-wave altermagnetic order in the surface layer of KV2Se2O. Atomically registered mapping reveals the spatial relationship between the two V sublattices and a density-wave lattice modulation, as well as real-space patterns consistent with the checkerboard antiferromagnetic order. Field-dependent spectroscopy further finds opposite energy shifts of the unidirectional quasiparticle excitations extending along two orthogonal crystal axes and a predominantly out-of-plane magnetic response. In momentum space, spin-sensitive quasiparticle interference imaging reveals a bias-reversing d-wave anisotropy between the symmetry-paired X and Y valleys. These results provide converging evidence for two-dimensional d-wave altermagnetism on the surface of KV2Se2O and demonstrate helical-edge-mode tunnelling as a route for atomic-scale spin sensing in quantum materials.

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Author information

Author notes

  1. These authors contributed equally: Zhuying Wang, Shuikang Yu, Xingkai Cheng, Xiaoyu Xiao

Authors and Affiliations

  1. Department of Physics, University of Science and Technology of China, Hefei, Anhui, China

    Zhuying Wang, Shuikang Yu, Wanru Ma, Yitian Ma, Feixiong Quan, Hongxi Song, Kunming Zhang, Yunmei Zhang, Qian Niu, Yang Gao, Zhenyu Wang & Xianhui Chen

  2. Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China

    Xingkai Cheng & Junwei Liu

  3. IAS Center for Quantum Matter, The Hong Kong University of Science and Technology, Hong Kong, China

    Xingkai Cheng & Junwei Liu

  4. Department of Materials Science & Engineering, Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China

    Xiaoyu Xiao, Xiangbiao Shi & Bin Xiang

  5. Hefei National Laboratory, University of Science and Technology of China, Hefei, China

    Wanru Ma, Qian Niu, Yang Gao, Bin Xiang, Zhenyu Wang & Xianhui Chen

  6. Department of Physics, The University of Texas at Dallas, Richardson, Texas, USA

    Wenhao Liu & Priti Yadav

  7. Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing, China

    Haohao Sheng & Zhijun Wang

  8. Low Temperature Physics Laboratory, College of Physics and Center of Quantum Materials and Devices, Chongqing University, Chongqing, China

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Corresponding authors

Correspondence to Bin Xiang, Junwei Liu, Zhenyu Wang or Xianhui Chen.

Supplementary information

Supplementary Information (download PDF )

Supplementary Notes 1-12, Supplementary Figs. 1-37, Supplementary Tables 1-2, and Supplementary References.

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Wang, Z., Yu, S., Cheng, X. et al. Atomic-scale spin sensing of a 2D d-wave altermagnet via helical tunneling. Nature (2026). https://doi.org/10.1038/s41586-026-11257-1

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  • DOIhttps://doi.org/10.1038/s41586-026-11257-1

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Original source Atomic-scale spin sensing of a 2D d-wave altermagnet via helical tunneling

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