  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 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, Jeff = 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.
