  Ultrafast and coherent generation of magnons is of great significance for
high-speed antiferromagnetic spintronics. One possible route is by
exciton-magnon pairwise optical excitation. To date, such exciton-magnon
transitions have been studied mostly by linear optical means in a limited
number of conventional three-dimensional antiferromagnets. Here we investigate
this correlated transition in van der Waals antiferromagnet MnPS$_3$ by using
resonant second-harmonic generation spectroscopy, a nonlinear optical probe
sensitive to the symmetry of electronic and magnetic excitations. Two
exciton-magnon peaks are observed, in line with the exciton-induced splitting
of magnon density of states predicted by a Koster-Slater type theory,
indicating significant exciton-magnon interactions. In addition, a large linear
magnetoelectric effect of excitons is observed. These findings provide renewed
understandings on the correlation effects in two-dimensional magnets with
enhanced quasiparticle scattering cross-sections, and point to potential
coherent control among charge, spin and orbital degrees of freedom in
two-dimensional magnets by optical means.
