单层WSi2P4中多晶型可调的自旋织构与激子结构

中文摘要 AI 辅助

同时具有直接带隙和强自旋-轨道耦合（SOC）的二维半导体对量子光电子学极具吸引力。利用第一性原理GW加Bethe-Salpeter方程（GW-BSE）计算，我们表明单层WSi2P4——MSi2X4家族中实验上可获取的成员——具有直接的K谷带隙以及强SOC。其三种竞争的多晶型（α、β和γ）均为直接带隙半导体，并被1.3 eV的迁移势垒动力学锁定。α和γ相的D3h对称性的σ_h镜面在布里渊区强制产生持续的自旋织构，在γ附近受带间SOC混合的弱调制，而极性的β相（C3v）则表现出Rashba自旋劈裂。SOC将双重简并的最低亮激子劈裂为暗态，并将原始吸收峰劈裂为两个峰（A和B），其相对亮度由K谷导带劈裂决定。α-WSi2P4表现出最亮的峰A，因为自旋相反分支的微小能带交叉可以打开自旋允许的辐射通道。这些结果确立了MSi2P4家族作为一个相可调平台，用于在单一材料系统中协同工程化自旋织构、能带劈裂和激子亮度。

英文摘要

Two-dimensional semiconductors that simultaneously possess a direct band gap and strong spin-orbit coupling (SOC) are highly attractive for quantum optoelectronics. Using first-principles GW plus Bethe-Salpeter equation (GW-BSE) calculations, we show that monolayer WSi2P4-an experimentally accessible member of the MSi2X4 family-hosts a direct K-valley gap together with strong SOC. Its three competing polymorphs (alpha, beta and gamma) are all direct-gap semiconductors and are kinetically locked behind 1.3 eV migration barriers. The sigma_h mirror plane of the D3h of alpha and gamma phases enforces a persistent spin texture across the Brillouin zone, weakly modulated near gamma by interband SOC mixing, whereas the polar beta phase (C3v) exhibits Rashba spin splitting. SOC splits the doubly-degenerate lowest bright exciton into dark states and splits the original absorption peak into two peaks (A and B), whose relative brightness is governed by the K-valley conduction-band splitting. alpha-WSi2P4 displays the brightest Peak A because a tiny band crossing of opposite-spin branches can open a spin-allowed radiative channel. These results establish the MSi2P4 family as a phase-tunable platform for the cooperative engineering of spin texture, band splitting, and excitonic brightness within a single material system.

发表机构

• Hangzhou Dianzi University（杭州电子科技大学）
• Southern University of Science and Technology（南方科技大学）
• Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences（中国科学院大学杭州高等研究院）

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