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

Abstract

While most devices thus far have utilized electrical charge modulation, the introduction of other physical degrees of freedom can provide numerous opportunities to design novel interfacial properties. In particular, strongly correlated electron systems of transition metal oxides provide optimal interfaces to integrate charge, spin, orbital, and lattice degrees of freedom. [6,7] So, correlated oxide heterostructures have a high potential to implement multi-state memories or multifunctional devices. [6][7][8] Most correlated oxides have high carrier densities and therefore their interactions at the heterointerfaces are significantly short. Previous studies have shown that, in the correlated oxide interfaces, charge modulations, [9][10][11] as well as magnetic, [12] orbital, [13] and structural [14] reconstructions occur within several atomic layers from the interface. There have been a few systematic studies of highelectron-mobility oxide heterostructures whose carrier densities are comparable to that of conventional semiconductors. [15,16] The short length scale of the interfacial reconstruction indicates 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 SrRuO 3 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 SrRuO 3 . 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.

Ferromagnetic insulating substrate for magnetic proximity studies: LaCoO3 thin film

“…Furthermore, its angle-integrated spectra showing no sharp quasiparticle peak near E F is consistent with the Fermiology of the 2 uc SRO from the previous study [32]. In contrast, for the film without a conducting layer, 2 uc SRO/10 uc LCO (green in figure 5(b)), there exists no spectral weight near the Fermi level, indicating the presence of a charging effect and incorrect measurement of the electronic structure compared to previous studies [32,33].…”

Nanoscale Enhancement of the Local Optical Conductivity near Cracks in Metallic SrRuO3 Film

“…And they can be grown with atomically flat surfaces due to step-flow growth modes; thus, we can achieve high-quality oxide heterostructures with an SRO bottom electrode layer . Recently, the physical properties of the SRO films started to attract much attraction, particularly due to their topological nature including topological Hall effects, Berry curvature physics, and anomalous Hall effects. − Such intriguing properties can be strongly affected by the strain, so controlling the SRO film properties using lattice mismatch with substrates has been an important topic. , So many researchers have attempted to grow SRO films on various substrates and look for emergent phenomena in the films. − However, SRO films on KTO substrates usually pose experimental difficulties, since they usually contain extended defects and cracks …”