Towards electrical-current control of quantum states in spin–orbit-coupled matter

Novel materials, which often exhibit surprising or even revolutionary physical properties, are necessary for critical advances in technologies. Simultaneous control of structural and physical properties via a small electrical current is of great significance both fundamentally and technologically. Recent studies demonstrate that a combination of strong spin–orbit interactions and a distorted crystal structure in magnetic Mott insulators is sufficient to attain this long-desired goal. In this topical review, we highlight underlying properties of this class of materials and present two representative antiferromagnetic Mott insulators, namely, 4d-electron based Ca₂RuO₄ and 5d-electron based Sr₂IrO₄, as model systems. In essence, a small, applied electrical current engages with the lattice, critically reducing structural distortions, which in turn readily suppresses the antiferromagnetic and insulating state and subsequently results in emergent new states. While details may vary in different materials, at the heart of these phenomena are current-reduced lattice distortions, which, via spin–orbit interactions, dictate physical properties. Electrical current, which joins magnetic field, electric field, pressure, light, etc as a new external stimulus, provides a new, key dimension for materials research, and also pose a series of intriguing questions that may provide the impetus for advancing our understanding of spin–orbit-coupled matter. This Topical Review provides a brief introduction, a few hopefully informative examples and some general remarks. It is by no means an exhaustive report of the current state of studies on this topic. (topical review)