Resonant Inelastic X-ray Scattering Study of Metallic Sr3(Ir1-xRux)2O7

Sr3Ir2O7 is a correlated Jeff=1/2 Mott insulator which is extremely susceptible to perturbation by chemical substitution. Doping with Ru on the B-site leads to a percolative metal-insulator transition near 33% Ru-substitution, but antiferromagnetic order persists well into the metallic phase with a pronounced maximum of TN around 45% doping (Dhital et al., Nat. Commun. 5, 3377 (2014)). Here we report resonant inelastic x-ray scattering results on Sr3(Ir1-xRux)2O7 samples within the metallic antiferromagnetic regime. We observe that spin wave excitations reminiscent of the undoped parent compound survive well into the metallic phase. The bandwidth is reduced as expected for the case where disorder quenches longer-range exchange interactions; however the zone center spin gap is strongly increased with continued Ru substitution. Potential explanations for this behavior and their implications for the exchange in the parent system are discussed.