Superconducting terahertz metamaterials mimicking electromagnetically induced transparency

We designed and fabricated planar terahertz (THz) metamaterials made from superconducting NbN films to mimic electromagnetically induced transparency (EIT) system. They are characterized using THz time domain spectroscopy over a temperature range from 8 to 300 K. High transmittance and large delay-bandwidth product at transparency window are demonstrated, which mainly arise from the enhanced coupling and decreased damping in superconducting state. The EIT-like spectral response could be tuned in a wide frequency range. By applying two dark resonators with different resonance frequencies coupled with a radiative resonator, we experimentally demonstrated the planar metamaterials mimicking four-level EIT system.