[论文解读] Spin - Phonon Coupling in Nickel Oxide Determined from Ultraviolet Raman Spectroscopy

Ece Aytan, Bishwajit Debnath+7 more|arXiv (Cornell University)|Oct 17, 2017

Transition Metal Oxide Nanomaterials参考文献 58被引用 63

一句话总结

该论文表明紫外拉曼光谱可以量化NiO中的自旋–声子耦合，揭示Ni自旋与LO声子的相互作用强于TO声子，并对声子能量的效应相反，与密度泛函理论趋势一致。

ABSTRACT

Nickel oxide (NiO) has been studied extensively for various applications ranging from electrochemistry to solar cells [1,2]. In recent years, NiO attracted much attention as an antiferromagnetic (AF) insulator material for spintronic devices [3-10]. Understanding the spin - phonon coupling in NiO is a key to its functionalization, and enabling AF spintronics' promise of ultra-high-speed and low-power dissipation [11,12]. However, despite its status as an exemplary AF insulator and a benchmark material for the study of correlated electron systems, little is known about the spin - phonon interaction, and the associated energy dissipation channel, in NiO. In addition, there is a long-standing controversy over the large discrepancies between the experimental and theoretical values for the electron, phonon, and magnon energies in NiO [13-23]. This gap in knowledge is explained by NiO optical selection rules, high Neel temperature and dominance of the magnon band in the visible Raman spectrum, which precludes a conventional approach for investigating such interaction. Here we show that by using ultraviolet (UV) Raman spectroscopy one can extract the spin - phonon coupling coefficients in NiO. We established that unlike in other materials, the spins of Ni atoms interact more strongly with the longitudinal optical (LO) phonons than with the transverse optical (TO) phonons, and produce opposite effects on the phonon energies. The peculiarities of the spin - phonon coupling are consistent with the trends given by density functional theory calculations. The obtained results shed light on the nature of the spin - phonon coupling in AF insulators and may help in developing innovative spintronic devices.

研究动机与目标

• 由于NiO在反铁磁绝缘体和自旋电子学中的相关性，激发对其自旋–声子耦合的研究。
• 开发一种紫外拉曼光谱方法，以量化NiO中的自旋–声子耦合系数。
• 识别哪种声子模（LO与TO）更强地与Ni自旋耦合，以及它们如何影响声子能量。
• 将实验结果与密度泛函理论趋势进行比较，以阐明NiO中的能量耗散通道。

提出的方法

• 使用紫外拉曼光谱来探测NiO并提取自旋–声子耦合系数。
• 分析Ni自旋与纵向光学（LO）声子和横向光学（TO）声子之间的耦合。
• 确定自旋–声子耦合对声子能量的影响，并给出移位的符号和量级。
• 将实验结果与密度泛函理论（DFT）预测进行比较，以确保一致性。

实验结果

研究问题

• RQ1 紫外拉曼光谱是否能量化 NiO 中的自旋–声子耦合系数？
• RQ2 Ni 自旋是否对 LO 和 TO 声子有不同的耦合？两者的能量移位符号各自为何？
• RQ3 在 NiO 中观察到的自旋–声子耦合趋势是否与密度泛函理论计算一致？
• RQ4 自旋–声子相互作用对反铁磁NiO的自旋电子学功能有何影响？

主要发现

• NiO 的自旋与 LO 声子的耦合比与 TO 声子更强。
• 自旋–声子耦合在 LO 和 TO 声子能量上产生相反的效应。
• 观察到的耦合趋势与密度泛函理论计算一致。