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Unexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures,J_eff= 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities.

 

The coupling between ferroelectric and magnetic order provides a powerful means to control magnetic properties with electric fields. In this study, we have investigated the magnetoelectric (ME) coupling in iridate-oxide based superlattices employing first-principles density functional theory (DFT) calculations. In particular, we have investigated several oxide superlattices, including (SrIrO 3 ) 1 –(CaTiO 3 ) 1 (SIO–CTO) and (SrIrO 3 ) 1 –(BaTiO 3 ) 1 (SIO–BTO), with an alternating single layer of SIO and CTO/BTO. We identify a very large ME coupling in SIO–BTO mediated by both lattice and electronic contributions. In comparison, moderate ME coupling constants are found in SIO–CTO. Further electronic and structural analyses reveal that the large ME coupling of SIO–BTO is caused by the large spin–orbit coupling of 5d iridium as well as the significant polarization induced in the SIO–BTO. Interestingly, we find that the ME coupling in SIO–BTO can further be enhanced by modulating epitaxial strain. These results suggest a route to significantly enhance the ME coupling effects, which might be applicable for other materials and practical applications.