Classical Analogue of Electromagnetically Induced Transparency with a Metal-Superconductor Hybrid Metamaterial

Metamaterials are engineered materials composed of small electrical circuits producing novel interactions with electromagnetic waves. Recently, a new class of metamaterials has been created to mimic the behavior of media displaying electromagnetically induced transparency (EIT). Here we introduce a planar EIT metamaterial that creates a very large loss contrast between the dark and radiative resonators by employing a superconducting Nb film in the dark element and a normal-metal Au film in the radiative element. Below the critical temperature of Nb, the resistance contrast opens up a transparency window along with a large enhancement in group delay, enabling a significant slowdown of waves. We further demonstrate precise control of the EIT response through changes in the superfluid density. Such tunable metamaterials may be useful for telecommunication because of their large delay-bandwidth products.

Figure 1

Transmittance and reflectance spectra. The transmittance shows a broad stop band originating from the coupling of the electromagnetic waves to the electric dipole mode of the wire, and three narrower resonancelike features that are associated with dark modes of the SRRs. (a) Experimental data at $T=2.6\mathrm{K}$. The FWHM bandwidth of the resonant features is 9, 10, and 1 MHz for the transmittance peaks and 2, 1, and 0.1 MHz for the reflectance features. (b) Simulation data when the metamolecule is horizontally displaced by 0.1 mm from the center of the waveguide. The dashed blue line is a simulation of the wire only. The labels $a\mathrm{\text{−}}d$ correspond to the current distributions in Fig. 2.

Figure 2

Current distributions in the wire and the split-ring resonators. (a) The electric dipole resonance of the wire. (b) The antisymmetric hybridization of the electric dipole resonance of the SRRs. (c) The symmetric hybridization of the magnetic dipole resonance of the SRRs. (d) The antisymmetric hybridization of the magnetic dipole resonance of the SRRs.

Figure 3

The group delay of the metamaterial obtained (a) from the experiment at $T=2.6\mathrm{K}$ (b) from the numerical simulations.

Figure 4

Temperature dependence of the measured (a) transmittance and (b) group delay of the metamaterial. The pronounced EIT features and the enhanced group delay at the lowest temperature vanish if the temperature is increased above the critical temperature of Nb. The inset in (a) shows the frequency of the rightmost EIT feature as a function of temperature. The inset in (b) shows the peak group delay at the rightmost EIT feature as a function of temperature. The incident power was $-20\mathrm{dBm}$.