Time Domain Terahertz Spectroscopy on the Electromagnons in NiI2

NiI₂, a type-II multiferroic material, has garnered significant attention recently. Optical measurements, such as second harmonic generation and linear dichroism, have demonstrated that the multiferroic state persists even at the ultrathin limit. The intrinsic coupling between helical spins and electric polarization results in the emergence of two electro-magnon modes at terahertz frequencies, where further investigation using all-optical pump-probe has revealed a giant chiral magnetoelectric response that is attributed to these oscillating modes. Given the oscillation frequencies at terahertz range, we employed time-domain terahertz spectroscopy (TDTS) to directly probe the two electro-magnons. We will provide evidence of their existence and uncovering potential coupling between the modes.