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

Helical-edge-mode tunnelling enables atomic-scale spin sensing of two-dimensional d-wave altermagnetism in KV2Se2O.

• Why it matters: Understanding altermagnetic order requires atomic-scale spin-sensitive measurements in both real and momentum space, a challenge that has yet to be achieved and is crucial for advancing quantum material research.
• What they did: The study used spin-sensitive quasiparticle interference imaging and scanning tunnelling microscopy with helical edge modes of a higher-order topological insulator to probe the surface layer of KV2Se2O, revealing spatial and momentum-space spin patterns.
• The result: Findings include real-space checkerboard antiferromagnetic order, opposite energy shifts of quasiparticles along orthogonal axes, and bias-reversing d-wave anisotropy, demonstrating helical-edge-mode tunnelling as a route for atomic-scale spin sensing.