AI 中文总结
本研究通过第一性原理计算揭示Ag$_{2}$BiO$_{3}$的$Pnn2$相为配体空穴驱动的键歧化绝缘体，且其高对称点附近存在由非简单对称性诱导的持久自旋织构，有望用于自旋电子学。
AI 中文摘要
本文采用第一性原理电子结构计算，探究了非中心对称（$Pnn2$）相Ag$_{2}$BiO$_{3}$所提出的键歧化绝缘态的起源。为阐明这一新型绝缘态，研究首先考察了最初提出的中心对称金属相（$Pnna$）Ag$_{2}$BiO$_{3}$。计算表明，该相中价态跳变的Bi$^{4+}$离子更适合用Bi$^{3+}\text{\textunderscore}\textit{L}$描述，其Bi-(6$s$)态完全填满，并存在一个配体空穴。然而声子计算显示，金属相（$Pnna$）是动力学不稳定的。通过氧八面体的呼吸畸变可实现结构稳定性，这一过程产生两个不等价的Bi位点，并将对称性降低至$Pnn2$相。电子结构计算进一步揭示，$Pnn2$相是一种键歧化绝缘体，其中Bi的名义电荷态可描述为：2[Bi$^{3+}\text{\textunderscore}\textit{L}$ (Bi$^{4+}$)] $\rightarrow$ Bi$^{3+}\text{\textunderscore}\textit{L}^{2-δ}$ (Bi1$^{5+}$) + Bi$^{3+}\text{\textunderscore}\textit{L}^δ$ (Bi2$^{3+}$)，凸显了配体空穴在驱动绝缘态形成中的关键作用。随后，研究还考察了包含自旋轨道耦合的绝缘相（$Pnn2$）Ag$_{2}$BiO$_{3}$的电子结构。我们的密度泛函理论（DFT）计算结合$\textbf{k}\textbf{.p}$模型哈密顿量分析表明，在非简单对称性的作用下，正交布里渊区的$X$和$Y$高对称点附近存在持久自旋织构，这使得Ag$_{2}$BiO$_{3}$成为自旋电子学应用的潜在候选材料。
英文摘要
The origin of the proposed bond disproportionated insulating state of the non-centrosymmetric ($Pnn2$) phase of Ag$_{2}$BiO$_{3}$ is explored using first principles electronic structure calculations. The novel insulating state is elucidated by first considering the initially proposed centosymmetric metallic ($Pnna$) phase of Ag$_{2}$BiO$_{3}$. Our calculations reveal that the valence skipping Bi$^{4+}$ ions in this phase are better described as Bi$^{3+}\underline{L}$ with completely filled Bi-(6$s$) states and a ligand hole. However, phonon calculations indicate that the metallic ($Pnna$) state is dynamically unstable. Structural stability is achieved through breathing distortions of the oxygen octahedra, resulting in two inequivalent Bi sites and a reduction of symmetry to the $Pnn2$ phase. Electronic structure calculations further reveal that the $Pnn2$ phase is a bond disproportionated insulator where the nominal charge state of Bi is described by : 2[Bi$^{3+}\underline{L}$ (Bi$^{4+}$)] $\rightarrow$ Bi$^{3+}\underline{L}^{2-δ}$ (Bi1$^{5+}$) + Bi$^{3+}\underline{L}^δ$ (Bi2$^{3+}$), highlighting the crucial role of ligand holes in driving the insulating state. Next we have investigated the electronic structure of Ag$_{2}$BiO$_{3}$ in the insulating ($Pnn2$) phase including spin-orbit coupling. Our density functional theory (DFT ) calculations complemented by ${\bf k.p}$ model Hamiltonian analysis reveal persistent spin-textures around the $X$ and $Y$ high symmetry points of the orthorhombic Brillouin zone imposed by non-symmorphic symmetry, positioning Ag$_{2}$BiO$_{3}$ as a promising candidate for spintronic applications.
