UC Santa Barbara

In the diverse catalog of `quantum materials' one of the most beguiling parameters is the spin-orbit coupling. This dissertation is concerned with how spin-orbit coupling effects exotic physics in correlated transition metal oxides. The materials described herein are all assembled from corner-sharing octahedra (Ir,Ru)O$_6$, and are hole-doped from the $d^5$ configuration, yet they contain a diversity of electronic and magnetic phases. A combination of resonant X-ray scattering and neutron scattering were employed to try to unravel the nature of the order and fluctuations in these materials.

First we examine the unusual Lifshitz transition in metallic Sr$_2$Ir$_x$Ru$_{1-x}$O$_4$, where we unveil a transition from itinerant to local moment behavior that might speak to quantum criticality. Second we explore the closely related compound Sr$_3$(Ir$_{1-x}$Ru$_x$)$_2$O$_7$, where the antiferromagnetism persists to remarkably high Ru content. Third is Sr$_3$Ir$_2$O$_7$F$_2$, which is like a fully hole-doped and distorted analog to Sr$_3$Ir$_2$O$_7$; there the spin-orbit excitons are thoroughly compared to theory. Last is (Ca$_x$Nd$_{1-x}$)$_2$Ir$_2$O$_7$, a tunable magnetic semimetal with potential for interesting topological states.