Tunable terahertz electromagnetically induced transparency based on a composite structure superconducting metamaterial

We experimentally present a tunable electromagnetically induced transparency (EIT)-like response in bright-bright mode resonators. In contrast to previous studies, we used NbN film and a gold film composite structure metamaterial. A significant slow-light effect could be observed at the transmission window, and the maximum group index could reach 100. As a variation in temperature alters the intrinsic ohmic loss of superconducting NbN film, a temperature-dependent transmittance and slow-light effect were observed. To better illustrate the physical mechanism of the two modes, a hybrid coupling model was introduced to fit the experimental transmission spectra and extract the characteristic parameters of sub-resonators. We found excellent agreement with experimental results. Our results provide deeper insight into the metamaterial analogs of an EIT-like response and offer an alternative approach for engineering slow-light devices, bandpass filters, and switches/modulators at terahertz frequencies.