d波交替磁性与拓扑态在Janus FeSeX (X = S, Te)单层中的共存
Coexistence of d-Wave Altermagnetism and Topological States in Janus FeSeX (X = S, Te) Monolayers
AI总结：
研究揭示Janus FeSeX单层中d波交替磁性与拓扑行为共存，通过第一性原理计算发现化学不对称性导致各向异性交换相互作用和动量依赖性自旋分裂，同时引入自旋轨道耦合后出现拓扑能带间隙和非平凡拓扑不变量。
摘要：
二维材料中非常规磁性与能带拓扑的相互作用已成为凝聚态物理的重要主题。本文通过第一性原理计算揭示了Janus FeSeX (X = S, Te)单层中d波交替磁性与拓扑行为的共存。Janus结构的化学不对称性破坏了平面外镜像和反演对称性，即使在没有自旋轨道耦合的情况下，也导致各向异性交换相互作用和动量依赖性自旋分裂，这是交替磁性的特征标志。声子色散分析证实了两种化合物的动态稳定性，而应变依赖性计算显示，通过双轴应变可以有效调节交替磁性交换分裂（Δ_s）的大小。当引入自旋轨道耦合时，在费米能级处出现有限的拓扑能带间隙，伴随量子化的自旋霍尔电导平台和非平凡拓扑不变量（自旋陈数=1，Z2=1）。这些发现确立了FeSeS和FeSeTe作为实现拓扑交替磁性和自旋轨道驱动的电荷-自旋转换的有希望的二维平台，从而为低损耗自旋电子器件开辟了新途径。
英文摘要：
The interplay between unconventional magnetism and band topology in two-dimensional materials has emerged as an important theme in condensed matter physics. Here, we present first-principles calculations that reveal the coexistence of d-wave altermagnetism and topological behavior in Janus FeSeX (X = S, Te) monolayers. The chemical asymmetry of the Janus structure breaks both out-of-plane mirror and inversion symmetries, leading to anisotropic exchange interactions and momentum-dependent spin splittings even in the absence of spin-orbit coupling, the defining signature of altermagnetism. Phonon dispersion analyses confirm the dynamical stability of both compounds, while strain-dependent calculations demonstrate that the magnitude of the altermagnetic exchange splitting ($Δ_s$) can be efficiently tuned by biaxial strain. When spin-orbit coupling is included, a finite topological band gap emerges at the Fermi level, accompanied by quantized spin Hall conductivity plateaus and nontrivial topological invariants (spin Chern number = 1, Z2=1). These findings establish FeSeS and FeSeTe as promising two-dimensional platforms for realizing topological altermagnetism and spin--orbit--driven charge--spin conversion, thus opening new avenues for low-dissipation spintronic devices.
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