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MgB2 has been recognized as a candidate material for fabricating superconducting nanowire single photon detectors with the expectation of having an operating temperature of the detector at 10-20 K. Preparation of ultrathin MgB2 films with high superconducting transition temperature TC is the first crucial step to achieve this goal. Here we present the hybrid physical-chemical vapor deposition of MgB2 superconducting films with thicknesses around 10 nm. The films are epitaxially grown on (111) MgO substrates. The TC of the films, including for a 6-nm-thick film, is found to be above 34 K, close to the bulk value of MgB2 (39 K). The normal-state resistivity at 42 K of a 10-nm-thick film is shown to be 3.1 μΩ cm, indicating that the film is relatively clean. The superconducting critical current density JC of the films has also been measured on strip lines patterned in the films. The JC of the 10-nm-thick film reaches 7.7 ×107 A/cm2 at 2 K, so far the highest value reported for MgB2 films of the same thickness. The high TC, low residual resistivity, and high JC of the ultrathin MgB2 films on MgO substrates suggest that these films have the potential in developing MgB2-based superconducting nanowire single photon detectors or other related superconducting devices.
Date of Publication: June 2013