Emergent Vibronic Excitations in the Magnetodielectric Regime of Ce₂O₃

The strong coupling between spin, lattice, and electronic degrees of freedom in magnetic materials can produce interesting phenomena, including multiferroic and magnetodielectric (MD) behavior, and exotic coupled excitations, such as electromagnons. We present a temperature-and magnetic field-dependent inelastic light (Raman) scattering study that reveals the emergence of vibronic modes, i.e., coupled vibrational and crystal-electric-field (CEF) electronic excitations, in the unconventional rare-earth MD material Ce2O3. The energies and intensities of these emergent vibronic modes are indicative of enhanced vibronic coupling and increased modulation of the dielectric susceptibility in the Néel state (TN≈6.2 K). The field dependences of the energies and intensities of these vibronic modes are consistent with a decrease of both the vibronic coupling and the dielectric fluctuations associated with these modes below TN. These results suggest a distinctive mechanism for MD behavior in Ce2O3 that is associated with a field-tunable coupling between CEF and phonon states.