Unveiling Nonlinearities of Electromagnetically Induced Transparency in a THz Metamaterial

ABSTRACT Electromagnetically induced transparency (EIT) in terahertz (THz) metamaterials relies on the coherent coupling between a radiative (bright) mode and a sub‐radiant (dark) mode. Understanding the dynamic interplay between the bright and dark modes is key to manipulating their mutual interference and hence the transparency. Here, we use nonlinear 2D‐THz spectroscopy to scrutinize the dynamics arising from the nonlinearities of the EIT‐like phenomenon in a metamaterial platform comprising two coupled resonators. From the temporal profiles of the nonlinear pump‐probe and photon‐echo signals, we found that the bright mode relaxation time is almost twice the time for the coherent exchange of energy between the two coupled resonators. The multi‐peak nature of the photon‐echo signal and the corresponding temporal signatures further provide a direct visualization of the interference between the dressed states that drives the transparency window in our THz metamaterial. A time‐resolved density‐matrix model accurately describes the observed features, including the cross‐peak behavior and the temporal dynamics, establishing the coherent mode coupling as the origin of the transparency window.