Emergence of high-temperature superconductivity at the interface of two Mott insulators

Interfacial superconductivity has manifested itself in various types of heterostructures: band insulator--band insulator, band insulator--Mott insulator, and Mott insulator--metal. We report the observation of high-temperature superconductivity (HTS) in a complementary and long-expected type of heterostructures, which consists of two Mott insulators, ${\mathrm{La}}₂{\mathrm{CuO}}₄$ (LCO) and ${\mathrm{PrBa}}₂{\mathrm{Cu}}₃{\mathrm{O}}₇$ (PBCO). By carefully controlling oxidization condition and selectively doping ${\mathrm{CuO}}₂$ planes with Fe atoms, which suppress superconductivity, we found that the superconductivity arises at the LCO side and is confined within no more than two unit cells (\ensuremath{\sim}2.6 nm) near the interface. A phenomenon of ``overcome the Fe barrier'' will show up if excess oxygen is present during growth. Some possible mechanisms for the interfacial HTS have been discussed, and we attribute HTS to the redistribution of oxygen.