Nonlinear phononic coupling in antiferromagnetic monolayer MnPS3

The nonlinear coupling between phonons, though being weak, can be manifested under high intensity laser pulse. Here we use first-principles calculations to identify the third-order nonlinear coupling between Raman and IR active phonons at $\mathrm{\ensuremath{\Gamma}}$ in antiferromagnetic ${\mathrm{MnPS}}_{3}$ monolayer. The couplings can be categorized into two types: type-A contains only ${A}_{1g}$, while type-B contains ${A}_{1g}$, as well as other representations of ${D}_{3d}$. The type-A coupling ${A}_{1g}(24){A}_{2u}^{2}(25)$ turns the magnetic point group of the system from ${D}_{3d}({D}_{3})$ to ${C}_{3v}({C}_{3})$ if spin-orbit coupling is ignored, and induces a phase transition from antiferromagnet to $i$-wave altermagnet. The ${E}_{u}(29\ensuremath{-}30)$ IR mode couples simultaneously with three Raman modes, and the polarization of light can be used to control the coupling between ${E}_{u}$ and ${E}_{g}$ mode. The degenerate IR modes [e.g., ${E}_{u}(10\ensuremath{-}11)$], when resonantly driven by circular polarized light pulse, can induce phonon orbital magnetic moment. The efficiency of transfer of energy and angular momentum from circular polarized light to phonon is discussed. Our work contributes to the understanding of light-induced magnetic phase transition in antiferromagnetic monolayers.