Two-Dimensional Superconductivity in Polycrystalline \({\text {Y}_{2}\text {O}_{2}\text {Bi}}\)

This chapter presents a report on the discovery of two-dimensional superconductivity in the \({\text {Bi}^{2{-}}}\) square net within polycrystalline \({\text {Y}_{2}\text {O}_{2}\text {Bi}}\) . Pristine \({\text {Y}_{2}\text {O}_{2}\text {Bi}}\) had previously been classified as non-superconducting in previous reports. However, a notable contrast emerged as superconductivity at approximately 2 K was induced by increasing the inter-net distance of \({\text {Bi}^{2{-}}}\) through the excessive incorporation of O into a hidden interstitial site. The bulk superconducting nature was evidenced through the observation of the Meissner effect and specific heat measurements. The emergence of superconductivity occurred by enhancing the distance between conductive inter-layers, without the need for carrier doping, which was scarcely observed in other superconductors. This suggests an unconventional superconducting mechanism. These concepts would be a novel route to induce superconductivity in layered compounds, shedding light on hidden superconducting compounds.