交变磁性α-MnTe中175-180 cm$^{-1}$拉曼特征的本质

中文摘要 AI 辅助

α-MnTe中的175 cm$^{-1}$拉曼模式长期以来被归因于该材料唯一对称允许的声子（$E_{2g}$），然而第一性原理计算始终将该模式置于100 cm$^{-1}$以下。近期研究对这一差异提出了三种相互竞争的解释：一种弱对称性降低（$D_{6h}\ ightarrow D_{3h}$）的声子、由本征空穴自掺杂产生的电子等离激元，或一种外在的MnTe$_2$杂质特征。在此，我们利用化学计量控制的分子束外延（MBE）解决了这一争议。我们有意改变黄铁矿型MnTe$_2$次生相相对于α-MnTe基体的比例。在这一系列样品中，175 cm$^{-1}$模式与MnTe$_2$的存在基本一一对应——凡检测到MnTe$_2$处该模式即出现，而在化学计量、单相α-MnTe中于标称激光功率下则缺失。当激光功率升高时，MnTe中也出现一个位于约175 cm$^{-1}$附近的额外模式；我们详细的温度依赖拉曼分析识别出激光功率烧灼区域接近一种畸变的MnTe相，并通过透射电子显微镜确认。这种直接的、生长控制的关联将该模式识别为外在的MnTe$_2$杂质特征或畸变的MnTe特征，而非本征声子或等离激元特征，为MBE生长的α-MnTe提供了一种实用的相纯度诊断方法，并澄清了哪些拉曼特征可可靠地归因于本征交变磁性相。

英文摘要

The 175 cm$^{-1}$ Raman mode in $α$-MnTe has long been assigned to the material's only symmetry-allowed phonon ($E_{2g}$), yet first-principles calculations consistently place this mode below 100 cm$^{-1}$. Recent works have offered three competing explanations for the discrepancy: a weak symmetry-lowering ($D_{6h}\rightarrow D_{3h}$) phonon, an electronic plasmon arising from intrinsic hole self-doping, or an extrinsic MnTe$_2$ impurity signature. Here we resolve this controversy using stoichiometry-controlled molecular beam epitaxy (MBE). We deliberately vary the fraction of pyrite-type MnTe$_2$ secondary phase relative to the $α$-MnTe matrix. Across this series, the 175 cm$^{-1}$ mode tracks the presence of MnTe$_2$ essentially one-to-one -- present wherever MnTe$_2$ is detectable, absent in stoichiometric, single-phase $α$-MnTe at nominal LASER powers. When LASER power is ramped up, an additional mode emerges in MnTe as well positioned close to $\approx$ 175 cm$^{-1}$; our detailed temperatures dependendent Raman analysis identifies the LASER power scorched region close to a distorted MnTe phase, confirmed via transmission electron microscopy. This direct, growth-controlled correlation identifies the mode as an extrinsic MnTe$_2$ impurity signature or as a distorted MnTe feature, rather than an intrinsic phonon or plasmon feature, providing a practical diagnostic for phase purity in MBE-grown $α$-MnTe and clarifying which Raman features can be reliably attributed to the intrinsic altermagnetic phase.

发表机构

• Indian Institute of Science（印度科学研究所）
• IIT Madras（印度理工学院马德拉斯分校）

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