Heteroepitaxial Control of Fermi Liquid, Hund Metal, and Mott Insulator Phases in Single‐Atomic‐Layer Ruthenates

Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities, and great efforts have been made to manipulate interfacial electronic phases. However, realizing such phases is often hampered by the inability to directly access the electronic structure information; most correlated interfacial phenomena appear within a few atomic layers from the interface. Here, atomic‐scale epitaxy and photoemission spectroscopy are utilized to realize the interface control of correlated electronic phases in atomic‐scale ruthenate–titanate heterostructures. While bulk SrRuO3 is a ferromagnetic metal, the heterointerfaces exclusively generate three distinct correlated phases in the single‐atomic‐layer limit. The theoretical analysis reveals that atomic‐scale structural proximity effects yield Fermi liquid, Hund metal, and Mott insulator phases in the quantum‐confined SrRuO3. These results highlight the extensive interfacial tunability of electronic phases, hitherto hidden in the atomically thin correlated heterostructure. Moreover, this experimental platform suggests a way to control interfacial electronic phases of various correlated materials. The interface control of electronic structure in single‐atomic‐layer ruthenates is demonstrated. Combining thin film epitaxy and photoemission spectroscopy, a method to study interfacial electronic phases of ultrathin heterostructures is developed. Fermi liquid, Hund metal, and Mott insulator phases of SrRuO3 are discovered, exclusively in the single‐atomic‐layer limit. This work suggests a general way to investigate ultrathin interfacial electronic systems.