Unveiling nonlinearities of electromagnetically induced transparency in a THz metamaterial

TL;DR

This study uses nonlinear 2D-THz spectroscopy to investigate the dynamic nonlinear interactions in a THz metamaterial exhibiting electromagnetically induced transparency, revealing detailed mode coupling and coherence effects.

Contribution

It provides the first detailed temporal analysis of nonlinearities in EIT-like phenomena in THz metamaterials using a time-resolved density matrix model.

Findings

Bright mode relaxation time is nearly twice the energy exchange time.

Photon-echo signals show multi-peak structures indicating interference between dressed states.

Coherent mode coupling is confirmed as the origin of the transparency window.

Abstract

Electromagnetically induced transparency (EIT) in terahertz (THz) metamaterials relies on the coherent coupling between a radiative (bright) mode and a subradiant (dark) mode. Understanding the dynamic interplay between the bright and dark modes holds the key to manipulate the mutual interference and hence the transparency. Here, we use nonlinear 2D-THz spectroscopy to scrutinize the dynamics through nonlinearities of the EIT-like phenomenon in a metamaterial platform that comprises of 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 photon-echo signal and the corresponding temporal signatures further provides 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.