Strong and selective magnon-phonon coupling in van der Waals antiferromagnet CoPS${}_3$

Abstract

The Raman scattering response of the biaxial antiferromagnet CoPS${}_3$ has been investigated as a function of both magnetic field and temperature. The peaks observed in the low-frequency spectral range (90--200~cm${}^{-1}$) have been identified as hybrid magnon--phonon excitations. The energies of the bare magnon and phonon modes, as well as the effective coupling strengths between different excitation pairs, have been determined. The strong and selective magnon--phonon interaction largely accounts for the pronounced splitting of two phonon-like modes observed at 152~cm${}^{-1}$ and 158~cm${}^{-1}$ in the antiferromagnetic phase of CoPS${}_3$. Based on the identification of bare magnon excitations and their magnetic-field dependence, we propose an updated set of parameters for the effective exchange ($J_{\mathrm{eff}}=9.9$~meV) and biaxial magnetic anisotropy ($D=4.3$~meV and $E=-0.7$~meV) and advocate for an apparent anisotropic $g$-factor ($g_x=g_y=2$, $g_z=4$) in the CoPS${}_3$ antiferromagnet.

9 pages, 6 figures, and supplemental material