Radiation-harvesting resonant superconducting sub-THz metamaterial bolometer

Summary form only given. The ability of metamaterials to concentrate energy of the incident radiation on the sub-wavelength scale has long been predicted to lead to new device applications with a significantly improved and even superior functionality; the concrete implementations are, however, only beginning to emerge. Here we show how combining the concept of a superconducting bolometer with the coherent metamaterial paradigm allows to create a very sensitive sub-THz radiation detector with high spectral selectivity of ν₀/Δν ~ 90.Figure 1a illustrates the solution. Our bolometer is based on asymmetrically-split-ring (ASR) metamaterial with a characteristic narrow BIT-like resonance which is extremely sensitive to Joule losses. It also belongs to a novel, special class of coherent metamaterials, where the resonant response results from the collective excitation of the entire metamaterial array underpinned by strong interactions between its metamolecules. The metamaterial design features an additional `signal line´ that electrically connects all metamolecules into a single network. We manufacture the metamaterial by patterning the thin niobium film on the sapphire substrate with standard UVphotolithography. The measurements are conducted by placing the metamaterial into the optical cryostat and cooling it down to temperature 5K. At such temperatures the niobium becomes superconducting which results in a sharp, low-loss metamaterial response in the sub-THz range (see Fig. 1b). We apply the bias of Vb = 4V (see Fig. 1a) to create a small hotspot within the metamaterial array (- 5% of the total area) where niobium is just below the superconducting transition point and is therefore very sensitive to Joule heating caused by the incident radiation. Strong interactions between the metamolecules that are typical to ASR metamaterial at its coherent resonance lead to channelling of radiation energy from the outer regions of the metamaterial- into the hotspot, thus allowing to combine the narrow spectral response with the extreme sensitivity, resulting in the overall very efficient radiation-detecting device.