[论文解读] Visualizing spin-polarization of an altermagnet KV$_2$Se$_2$O via spin-selective tunneling

Guofei Yang, Chuang Li+14 more|arXiv (Cornell University)|Mar 23, 2026

Topological Materials and Phenomena被引用 0

一句话总结

本文使用 SmB6 纳米线探针的自旋选择性隧穿显微镜来可视化 KV2Se2O 的 d-wave 变磁体自旋分裂，并验证与变磁性一致的动量空间自旋极化。

ABSTRACT

Altermagnetism, a recently identified magnetic phase that combines vanishing net magnetization with momentum-dependent spin splitting, challenges the conventional dichotomy between ferromagnets and antiferromagnets. While several candidate materials have been proposed, direct experimental evidence linking crystal symmetry, electronic structure and d-wave spin polarization remains scarce. Here we report the visualization of a metallic d-wave altermagnet in KV2Se2O. Through spin-selective scanning tunneling microscopy powered by a topological insulator tip, we uncover symmetry-protected momentum-dependent spin splitting that follows a characteristic d-wave form factor. Our results establish KV2Se2O as a tunable platform to study the interplay between spin-valley locking, Fermi-surface instability and unconventional magnetism, and open a pathway toward symmetry-engineered spintronics without net magnetization.

研究动机与目标

• Motivate the search for direct real-space evidence of altermagnetism in KV2Se2O.
• Demonstrate symmetry-protected, momentum-dependent spin splitting in a metallic altermagnet.
• Provide a minimally invasive, spin-resolved probe to visualize AM band structure at the surface.
• Compare spin-sensitive and spin-insensitive tunneling to isolate intrinsic AM signatures.

提出的方法

• Use SmB$_6$ nanowire STM tips as intrinsic spin filters to achieve spin-polarized tunneling.
• Acquire spin-sensitive dI/dV maps and conventional dI/dV maps at ~5 K on KV$_2$Se$_2$O surface.
• Perform Fourier transforms of quasi-particle interference (QPI) patterns to extract momentum-space spin-split bands.
• Model the AM+SDW band structure with a minimal d-wave AM model and compare to QPI data.
• Analyze impurity-induced standing waves with both W-tip (spin-insensitive) and SmB$_6$-tip (spin-sensitive) to reveal spin polarization in real space.

Figure 1: Crystal structure and basic surface properties. (A) Unit cell of KV 2 Se 2 O. (B) Projection of K and V-plane with the shade purple circles represent K atoms, blue and red balls represent V atoms with local spin point down and up. Lattice constant $a$ = 3.966 Å. (C) The cleaved surface of

实验结果

研究问题

• RQ1 Does KV$_2$Se$_2$O exhibit momentum-dependent spin splitting consistent with d-wave altermagnetism on its surface?
• RQ2 Can spin-selective tunneling with a topological Kondo insulator tip reveal intrinsic AM spin textures without perturbing the system?
• RQ3 Do impurity-induced QPI patterns show direction-dependent spin polarization between q$_x$ and q$_y$?
• RQ4 How does the SDW order interact with altermagnetic spin splitting on the surface?

主要发现

• Observes symmetry-protected momentum-dependent spin splitting following a d-wave form factor.
• finds AM spin-splitting magnitude around ~1.8 eV, with SDW gap ≈40 meV.
• QPI analysis with W-tip and SmB6-tip shows spin-dependent anisotropy between q$_x$ and q$_y$ directions.
• A π phase shift in QPI between orthogonal directions emerges with spin-sensitive tunneling, indicating opposite spin polarization in d$_{xz}$ and d$_{yz}$ bands.
• Theoretical modeling of a minimal d-wave AM model agrees well with the observed QPI patterns.
• Spin-polarized tunneling confirms KV$_2$Se$_2$O as a platform to study AM spin textures and potential spintronic applications.

Figure 2: Band structure of KV 2 Se 2 O. (A) Differential conductance (d $I$ /d $V$ ) map measuring $35\times 35$ nm 2 , obtained at a bias of 40 mV ( $V_{\text{mod}}=2$ mV). (B) FFT of the map in (A) , revealing the dominant scattering vector $q_{x}$ and $q_{y}$ (indicated by the white arrow). Gree