Opto-spintronics in atomic-layer materials

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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.