Current-Noise Superconducting Bolometer for Terahertz Waves

摘要

An advantage of superconducting detectors is a much lower noise in comparison to their semiconductor counterparts. We have studied the magnitude and spectrum of electric noise in thin superconducting NbN nanostrips carrying a subcritical current. Analysis of the experimental data suggests that the noise appears due to fluctuations in the two-dimensional vortex gas below the Kosterlitz-Thouless phase transition. Basing on this picture of the noise mechanism, we proposed a novel terahertz detector. The novelty is the use of the noise, which generally hampers the performance of conventional detectors, as the physical quantity that itself senses radiation. Our detector was patterned from a thin NbN superconducting film and integrated in a planar log-periodic antenna. The detector operates at 4.2 K in the current-carrying superconducting state. Optically measured noise-equivalent power amounted at 10~(-13) W / Hz and is likely to improve at lower temperatures.