Negative Refraction in a Photon-Magnon Hybrid

Artificially fabricated negative-refractive-index (NRI) metamaterials have been realized based on the negative values of both the permittivity and permeability of a given structure, the so-called double negative-material criterion. Here, we experimentally demonstrated, through the single-negative material criterion, the occurrence of the NRI in a photon-magnon hybrid composed of an Yttrium Iron Garnet (YIG) film and an inverted split-ring resonator (ISRR). The NRI signature was found by extracting S21 and S11 parameters versus the frequency of microwave ac currents and the static field strength from the sample. In order to obtain the underlying NRI mechanism from the YIG/ISRR hybrid structure, we analytically derived the permittivity and permeability along with the refractive index using series impedance (Z_se) and shunt admittance (Y_sh) based on an appropriate circuit model. The analytical model, which was in quantitative agreement with the experimental NRI values, revealed that the single-negative-material criterion is met at/near the intersection of resonance frequencies of YIG and the ISRR under specific field conditions. The advantages of NRI established in the photon-magnon hybrid are the tunability of NRI magnitude as well as the magnetic-field-controllable on-off switching in a fabricated structure. This work can provide a new paradigm for the realization of magnetic-field-controllable NRI metamaterials.