We use resonant elastic and inelastic X-ray scattering at the Ir-L3​ edge
to study the doping-dependent magnetic order, magnetic excitations and
spin-orbit excitons in the electron-doped bilayer iridate
(Sr1−x​Lax​)3​Ir2​O7​ (0≤x≤0.065). With increasing
doping x, the three-dimensional long range antiferromagnetic order is
gradually suppressed and evolves into a three-dimensional short range order
from x=0 to 0.05, followed by a transition to two-dimensional short range
order between x=0.05 and 0.065. Following the evolution of the
antiferromagnetic order, the magnetic excitations undergo damping, anisotropic
softening and gap collapse, accompanied by weakly doping-dependent spin-orbit
excitons. Therefore, we conclude that electron doping suppresses the magnetic
anisotropy and interlayer couplings and drives
(Sr1−x​Lax​)3​Ir2​O7​ into a correlated metallic state hosting
two-dimensional short range antiferromagnetic order and strong
antiferromagnetic fluctuations of Jeff​=21​ moments, with
the magnon gap strongly suppressed.Comment: 6 Pages, 3 Figures, with supplementary in Sourc