Opto-spintronics in atomic-layer materials

高效的磁子光生成为实现超快光学自旋电子学的重要手段。作为MnPS3中Frenkel激子的一个磁振子边带，激子-磁振子对的直接光激发为在二维范德华(VDW)反铁磁体中产生磁子和操纵自旋提供了一种很有前途的方法。然而，成对激发的细节以及由此产生的磁子的性质还远未被很好地理解。利用共振二次谐波产生谱并结合群论分析，我们在MnPS3的磁振子边带内发现了两个子带，它们起源于激子-磁振子相互作用引起的磁振子密度分裂。我们发展的一个理论，结合模型和公式，再现了观测到的边带线形，并为激子扰动下的非常规磁振子分裂提供了定量证据。我们在常规三维反铁磁体中没有发现的MnPS3中激子诱导的大磁振子分裂的发现，表明了二维VDW磁系统中电荷、自旋和轨道自由度之间的增强关联。我们的研究还表明了激子-磁振子激发对超快多模磁振子的潜在控制作用。

Efficient photogeneration of magnons is important for realizing ultrafast optospintronics. Direct photoexcitation of exciton-magnon pairs, observed as the one-magnon sideband of Frenkel exciton in MnPS3, suggests a promising approach to generate magnons and manipulate spins in two-dimensional (2D) van der Waals (vdW) antiferromagnets. However, the details of the paired excitation as well as the properties of magnons so generated are far from being well understood. Using resonant second-harmonic generation spectroscopy combined with group theoretical analysis, we identified two subbands within the magnon sideband of MnPS3, originating from the splitting of magnon density of states due to significant exciton-magnon interactions. A theory developed by us, incorporating modeling and formulation, reproduces the observed sideband lineshape and offers quantitative evidence for the unconventional magnon splitting under perturbation by exciton. Our finding of the large exciton-induced magnon splitting in MnPS3, not identified in conventional three-dimensional antiferromagnets, suggests the enhanced correlation among charge, spin and orbital degrees of freedom in the 2D vdW magnetic systems. Our study also suggests the potential ultrafast multimode magnon control through the exciton-magnon excitations.