Detection of s-wave superconductivity on monolayer CuO$_{\mathrm{2}}$ films on Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8+\delta }}$.

High temperature superconductivity emerges when the CuO$_{\mathrm{2}}$ layer touches the doped charge reservoir blocks. The redistributed charge carriers at these interfaces condense into coherent Cooper pairs, albeit the exact underlying mechanism is still highly controversial. Targeting at this, we have mimicked the CuO$_{\mathrm{2}}$/charge reservoir interface by depositing the monolayer CuO$_{\mathrm{2}}$ films on optimal doped Bi$_{\mathrm{2}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{2}}$O$_{\mathrm{8+\delta }}$ substrates. Direct investigation on these superconducting CuO$_{\mathrm{2}}$ films, however, yields results in stark contrast with the common recognition. Despite of the well-known V shaped pseudogap, a U shaped gap is identified. This U shaped gap disappears at $T_{C}$ and is indifference to K, Cs and Ag adsorbates, in line with the traditional \textit{s-wave} superconductivity. In view of these results, we propose that superconductivity in cuprates may indeed stem from the modulation doping induced two dimensional hole liquid, which is confined in the CuO$_{\mathrm{2}}$ layers.