Spatial inhomogeneity and the metal-insulator transition in Ca_{3}(Ru_{1−x}Ti_{x})_{2}O_{7}

Turning a pristine Mott insulator into a correlated metal by chemical doping is a common procedure in strongly correlated materials physics, e.g., underlying the phenomenology of high-T_{c} cuprates. The ruthenate bilayer compound Ca_{3}Ru_{2}O_{7} is a prominent example of a reversed case, namely, a correlated metal at stoichiometry that realizes a transition into an insulating state via Ti doping. We here investigate this puzzling metal-insulator transition (MIT) by first-principles many-body theory and elucidate a challenging interplay between electronic correlations and symmetry breaking on the Ru sublattice. While average effects on the Ca_{3}Ru_{2}O_{7} crystal structure are still relevant, the key to the MIT is the cooperation of electronic correlations with the spatial inhomogeneity in the defect regime. Together they give rise to the emergence of site-selective Mott criticality and competing orbital-ordering tendencies.