Graphene-based terahertz superconducting Josephson junction detector

The Purple Mountain Observatory of the Chinese Academy of Sciences cooperated with the 13th Research Institute of China Electronics Technology Group to take the lead in the world to realize a terahertz high-sensitivity detector based on the superconductor-graphene-superconductor (SGS) Josephson junction. The related research results are titled “A terahertz detector based on superconductor-graphene-superconductor Josephson junction” and were recently published online in the international carbon materials journal “Carbon”.

The terahertz band (0.1-10 THz), between microwave and infrared, is a unique “window” for observing early distant objects, cold and dark objects, and optically invisible objects obscured by dust. Technically, the terahertz band is in the transition region from electronics to photonics, and is an electromagnetic spectrum to be fully developed, and researchers continue to try new materials and technologies to achieve astronomical detection of background limit sensitivity. In recent years, the high-sensitivity detector technology based on two-dimensional graphene materials has been developed rapidly, especially the SGS Josephson junction superconducting detector combining two-dimensional graphene material and superconducting material has been realized in the microwave band, and is expected to expand to the terahertz spectrum, opening up a new way for the development of high-sensitivity terahertz superconducting detector.

The study led by the Purple Mountain Observatory used a double-layer graphene film grown by high-temperature pyrolysis as a microbridge to connect two niobium (Nb) superconducting electrodes, and developed the first high-sensitivity superconducting detector based on two-dimensional graphene material SGS Josephson junction in the terahertz spectrum. When the length of the graphene film was shortened to the submicron scale, the Josephson tunneling phenomenon caused by the proximity effect between the niobium superconducting electrode and the graphene microbridge was successfully observed. Terahertz radiation signals can be detected by monitoring the changes in current in graphene microbridges due to absorbed radiation. The researchers used a low-noise superconducting quantum interferometer (SQUID) as the readout circuit of the SGS Josephson junction detector, and measured the optical noise equivalent power (NEP) of 2.5-5×10-16 W/Hz 0.5 in the 1.4 THz band and 0.1-0.6K temperature zone, which reached the background limit detection sensitivity of ground observation in this frequency band. This study is the first time in the world to realize the SGS Josephson junction high-sensitivity detector technology in the terahertz spectrum, and the research results expand the application direction of two-dimensional graphene materials, and provide a new technical way for the development of large-scale array terahertz detectors for astronomical applications.

Schematic diagram of terahertz superconductor-graphene-superconductor Josephson junction detector (left) and measured detector sensitivity (optical noise equivalent power/NEP) with ambient temperature at different bias pressures (right)

The first author and corresponding author of the paper is Miao Wei, a researcher at the Purple Mountain Observatory Millimeter and Submillimeter Wave Technology Laboratory. This research was supported by the National Natural Science Commission Outstanding Young Science Fund Project and the Key Technology R&D Team of the Chinese Academy of Sciences. (Source: Purple Mountain Observatory, Chinese Academy of Sciences)

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