Microwave One-way Transparency by Large Synthetic Motion of Magnetochiral Polaritons in Metamolecules

Abstract

We observe microwave nonreciprocal one-way transparency via ultrastrongly-coupled magnetochiral polaritons (MChPs) in a metamolecule at room temperature. The experimental results using MCh metamolecules with simultaneous breaking of time-reversal and space-inversion symmetries are reproduced by numerical simulations. Based on effective polarizability tensor analyses, we verify massive synthetic motion of MChPs as an origin of the one-way transparency. This study paves a way to hybrid quantum systems and synthetic gauge fields using metamaterials.

Figures (4)

• Figure 1: (a) A photo of the MCh metamolecule consisting of YIG magnetic meta-atom and Cu chiral meta-atom. A white bar corresponds to 5 mm. (b) Microwave measurement setup. The metamolecule is oriented along the $y$-axis in the WR-90 waveguide. A DC magnetic field $\mu_{0} H_{\rm ext}$ up to 500 mT is applied in the +$z$ direction using an electromagnet. (c) $x$-$y$ plane views of the metamolecule. The coil's endpoints are arranged to have 180-degree rotational symmetry with respect to the $x$-axis. (d) A cross-sectional view in the $x$-$y$ plane of the WR-90 waveguide. Red arrows correspond to the AC electric fields of the TE$_{10}$ mode.
• Figure 2: (a) Measured $T^{+}$ (red) and $T^{-}$ (blue) spectra at various external DC magnetic fields, $\mu_{0} H_{\rm ext}$ of 0 - 500 mT. Black and white triangles indicate dips caused by Mie-coupled MChPs. (b) Numerically calculated $T^{+}$ (red) and $T^{-}$ (blue) spectra at various external DC magnetic fields of 0 - 500 mT. The phenomenological Gilbert damping parameter $\alpha$ is set to 0.004 in the calculation.
• Figure 3: 2D plots of experimentally observed (a) $T^{-}$ and (b) $T^{+} - T^{-}$ of the $y$-axis-oriented metamolecule, and (c) $T^{-}$ and (d) $T^{+} - T^{-}$ of the $x$-axis-oriented metamolecule as a function of $\mu_{0} H_{\rm ext}$ (horizontal) and frequency (vertical).
• Figure 4: Effective polarizabilities evaluated from numerical simulation of the $y$-axis-oriented metamolecule using $y$-polarized waves. Frequency versus extracted (a) $\alpha_{yy}^{\rm ee} \omega Z_0$ (red) and $\alpha_{xx}^{\rm mm} \omega Z_0^{-1}$ (blue), (b) $\alpha_{yy}^{\rm me} \omega$ (gold) and $\alpha_{xx}^{\rm em} \omega$ (cyan), (c) $\alpha_{xy}^{\rm ee} \omega Z_0$ (black) and $\alpha_{yx}^{\rm mm} \omega Z_0^{-1}$ (pink), (d) $\alpha_{yx}^{\rm em} \omega$ (green) and $\alpha_{xy}^{\rm me} \omega$ (purple). (e) MO and (f) moving effects of the $y$-axis-oriented metamolecules (blue) are compared with those of the $x$-axis-oriented metamolecules (red). Solid and dashed lines present real and imaginary parts, respectively. External magnetic field $\mu_{0} H_{\rm ext}$ is 400 mT.