  Two-dimensional (2D) magnetic systems possess versatile magnetic order and
can host tunable magnons carrying spin angular momenta. Recent advances show
angular momentum can also be carried by lattice vibrations in the form of
chiral phonons. However, the interplay between magnons and chiral phonons as
well as the details of chiral phonon formation in a magnetic system are yet to
be explored. Here, we report the observation of magnon-induced chiral phonons
and chirality selective magnon-phonon hybridization in a layered zigzag
antiferromagnet (AFM) FePSe$_3$. With a combination of magneto-infrared and
magneto-Raman spectroscopy, we observe chiral magnon polarons (chiMP), the new
hybridized quasiparticles, at zero magnetic field. The hybridization gap
reaches 0.25~meV and survives down to the quadrilayer limit. Via first
principle calculations, we uncover a coherent coupling between AFM magnons and
chiral phonons with parallel angular momenta, which arises from the underlying
phonon and space group symmetries. This coupling lifts the chiral phonon
degeneracy and gives rise to an unusual Raman circular polarization of the
chiMP branches. The observation of coherent chiral spin-lattice excitations at
zero magnetic field paves the way for angular momentum-based hybrid phononic
and magnonic devices.
