Ruthenates, iridates, and relativistic Mott insulators

Layered ruthenates, rhodates, and iridates provide a unique setting in which electronic correlations, orbital structure, and spin-orbit coupling all act on comparable energy scales. As a result, these materials host a rich range of phenomena, from unconventional superconductivity and correlated metallic behavior to relativistic Mott insulating states, and have become a fertile arena for exploring how spin, orbital, and lattice degrees of freedom are intertwined in quantum matter.

Our work has helped define several key aspects of this field. In Sr2​RuO4​, we established the Fermi surface as a critical benchmark for ARPES, clarified the role of surface states and surface reconstruction, and traced the progression from surface to bulk electronic structure in the normal state. We then showed that strong spin-orbit coupling substantially reshapes the Fermi surface and dispersion of both Sr2​RuO4​ and Sr2RhO4​, culminating in the demonstration of spin-orbital entanglement and the breakdown of a simple singlet-triplet description in Sr2​RuO4​. In the iridates, our studies established Na2​IrO3​ and Sr2​IrO4​ as paradigmatic relativistic Mott insulators and revealed the role of spin-orbit coupling in the metal-insulator transition of Sr2​IrO4​. More recently, in the Mott insulator Ca2​RuO4​, we uncovered the electronic response at a current-induced insulator-to-metal transition.