NTT Basic research laboratories have succeeded in fabricating superconducting tunnel junctions using magnesium diboride (MgB₂) and observed, for the first time, supercurrent at 20K (Figs. 1 and 2). This temperature is the highest among artificially fabricated tunnel junctions and can be easily reached by using commercial compact cryocoolers without using liquid helium. Superconducting tunnel junctions are the key components of devices for superconducting electronic applications such as high-sensitive magnetic sensors (SQUID), electromagnetic wave detectors and so on. These results will enlarge the area of the superconducting electronic applications.

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