自旋电子太赫兹发射器中电荷与自旋动力学的时间依赖密度泛函理论研究

中文摘要 AI 辅助

基于铁磁/重金属异质结构的自旋电子太赫兹（THz）发射器提供了高效的宽带太赫兹辐射源，然而超快自旋输运与电荷重新分布之间的微观关系仍未完全理解。在此，我们采用时间依赖密度泛函理论，在实空间和实时间上解析Co/Pt和Co/W双层结构中的耦合电荷、自旋和磁化动力学。尽管层间自旋电流动力学在定性上相似，这两种异质结构却表现出显著不同的层间电荷转移：Co/Pt显示出相对较小且部分反向的从Pt到Co的转移，而Co/W则表现出更大且持续的从Co到W的转移。我们将这些差异归因于材料依赖的基态电子结构以及光激发载流子可访问的自旋和轨道分辨的相空间。自旋分辨动力学进一步揭示了自旋-轨道介导的重新分布与光诱导的位点间自旋转移的共存，包括两种系统中共同存在的从重金属到Co的延迟少数自旋转移。虽然净电子自旋角动量在层间转移，但我们发现没有相应的净电子轨道角动量转移。在Co/W中，电子密度从间隙态到原子中心态的持续重新分布还提供了光诱导电子局域化的强有力证据。这些结果表明，超快自旋输运并不能唯一决定自旋电子太赫兹发射器中的电荷或角动量重新分布，后者反而关键依赖于材料特定的电子相空间。

英文摘要

Spintronic terahertz (THz) emitters based on ferromagnet/heavy-metal heterostructures provide efficient broadband sources of THz radiation, yet the microscopic relation between ultrafast spin transport and charge redistribution remains incompletely understood. Here, we employ time-dependent density functional theory to resolve the coupled charge, spin, and magnetization dynamics of Co/Pt and Co/W bilayers in real time and space. Despite qualitatively similar interlayer spin-current dynamics, the two heterostructures exhibit markedly different interlayer charge transfer: Co/Pt shows a relatively small and partially reversed transfer from Pt to Co, whereas Co/W exhibits a larger and persistent transfer from Co to W. We trace these differences to the material-dependent ground-state electronic structure and the spin- and orbital-resolved phase space accessible to photoexcited carriers. Spin-resolved dynamics further reveal coexisting spin-orbit-mediated redistribution and optically induced intersite spin transfer, including a delayed minority-spin transfer from the heavy metal to Co common to both systems. While net electronic spin angular momentum is transferred between the layers, we find no corresponding net transfer of electronic orbital angular momentum. In Co/W, the persistent redistribution of electronic density from interstitial to atom-centered states additionally provides strong evidence for light-induced electronic localization. These results demonstrate that ultrafast spin transport does not uniquely determine charge or angular-momentum redistribution in spintronic THz emitters, which instead depends critically on the material-specific electronic phase space.

发表机构

• Institute of Physics, Academia Sinica（中央研究院物理研究所）

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