Local electromagnetic field enhancement in resonant metamaterials is useful for efficient generation of nonlinear phenomena; however, the field enhancement is suppressed by losses of nonlinear elements in metamaterials. For overcoming this issue, we investigate the nonlinear response of an electromagnetically induced transparency like metasurface loaded with gas as the nonlinear element. To induce nonlinearity in the gas associated with discharges, an electromagnetic wave with a modulated amplitude is incident on the metasurface. The measured waveform and spectrum of the transmitted electromagnetic wave, along with light emission from the discharge microplasma, reveal that frequency mixing can occur on the metasurface. The parameter dependence of the conversion efficiency of the frequency mixing phenomenon shows that the efficiency is determined almost entirely by the ratio of the duration of microplasma generation to the modulation period of the incident wave amplitude. This result implies that the frequency mixing is derived from a binary change in the transmittance of the metasurface caused by the generation and quenching of the microplasma.There has been considerable interest in enhancing nonlinear phenomena using metamaterials. 1 When an electromagnetic wave is incident on a resonant metamaterial, the electromagnetic energy becomes compressed into a small volume in the metamaterial. If a nonlinear element is excited by the enhanced local electromagnetic field, nonlinear phenomena can be efficiently generated. To date, various nonlinear phenomena, such as frequency conversion, 2-18 power-dependent responses, [19][20][21][22][23][24][25] and nonlinear wave propagation [26][27][28][29][30][31] have been investigated.The enhancement factor of the local electromagnetic field in a resonant metamaterial is inversely related with the losses in its unit structure. In the optical region, nonlinear dielectric resonators 7-9 would be suitable for the unit structure, since nonlinear dielectrics possess small losses. In contrast, lower frequency regions, including microwave and terahertz, require electronic devices, such as varactor diodes, to be introduced as nonlinear elements. 1 These electronic devices have relatively high losses, which suppress the local electromagnetic field enhancement.In this study, we investigate a metasurface loaded with gas as a nonlinear element to develop a method for preventing the suppression of the resonant enhancement of local electromagnetic fields. Gases have low linear losses, and exhibit discharges under the application of a strong electric field. Thus, we consider gases to be suitable for the efficient generation of nonlinear phenomena in resonant metamaterials, especially at lower frequencies. In addition, discharges cause abrupt changes in the electromagnetic characteristics of gases. Therefore, it may be possible to generate highly nonlinear phenomena in gas-loaded resonant metamaterials. In this paper, we show that frequency mixing can be generated using the a) Electronic mail: t...