Doping-driven robust superconductivity in tungsten for single-photon detection

Elemental superconductors are widely applied in quantum electronic devices, providing a homogenous research platform for both fundamental science and revolutionary technologies. However, their application in superconducting electronics remains a challenge due to the ultralow operation temperatures and suboptimal stability. Here, we develop a nitrogen-doping strategy to enhance the superconductivity of ultrathin amorphous superconductors for single-photon detection. The interstitial N dopants induce the amorphization of W, resulting in an enhanced superconducting transition temperature of 4.4 K from 0.01 K (α-W). Furthermore, the surface nitroxide passivation layer ensures smooth and homogeneous topography at the wafer scale and provides strong chemical stability for nanodevice fabrication in a 6.0-nm-thick nitrogen-doped amorphous tungsten (NAW) film. Consequently, we achieve NAW-based infrared SNSPDs with saturated quantum efficiency at an operation temperature of >1 K. This doping strategy can be applied to more elemental superconductors and, thus, promote their practical use in electronic devices.