High-mobility carriers and superconductivity at the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">SrNbO</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>−</mml:mo><mml:msub><mml:mi mathvariant="normal">SrTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> interface

Interfaces between transition-metal oxides can host two-dimensional electron gases (2DEGs) that exhibit intriguing quantum phenomena. The interfacial 2DEG system has attracted significant attention due to its versatile properties and tunability. In this study, we present the discovery of a high-mobility 2DEG characterized by well-developed Shubnikov-de Haas oscillations, alongside superconductivity at temperatures below 230 mK, in a heterostructure comprising bulk-metallic ${\mathrm{SrNbO}}_{3}$ on ${\mathrm{SrTiO}}_{3}$. The 2DEG is featured with extremely low carrier density for the quantum oscillations, and the superconductivity with two-step behaviors in various transport properties. Both the 2DEG and the superconductivity exhibit a common dependence on the thickness of the ${\mathrm{SrNbO}}_{3}$ layer. The dependence underscores the crucial role of epitaxial strain within the metallic layer on these two phenomena. Our findings introduce a novel platform for investigating interfacial high-mobility 2DEGs coexisting with superconductivity, with the bulk-metallic components of ${\mathrm{SrNbO}}_{3}$ playing a pivotal role in these heterostructures.