Microwave Funneling through Sub-10 nm Nanogaps

We demonstrate microwave funneling through metallic gaps of nanometer-scale width, corresponding to λ/10 000 000. For achieving both resonant transmission and strong confinement of microwaves, we fabricate two types of samples with an extreme aspect ratio: 300 nm wide, 3.5 mm long slots and sub-10 nm wide rectangular rings with a perimeter of 6.5 mm. Considering the peak transmittance value of 45% and the small coverage ratio of transparent area in the nanogap surface, we can infer a giant intensity enhancement factor of up to 25 million inside the nanogaps. The polarization extinction ratio up to 20 dB indicates that the microwave transmission originates from capacitive coupling of the induced charges at the sidewalls of a metallic gap. We also measure terahertz transmittance and observe a convergence to the microwave range. Our work represents the highest field enhancement recorded for the microwave regime, made possible by wafer-scale-length nanogaps matching the wavelengths, with future applications in centimeter wave nonlinearities and enhanced detection sensitivities.