Unidirectional spin density wave state in electron doped Sr₂IrO₄

Materials that exhibit both strong spin orbit coupling and appreciable electron correlation effects are predicted to host numerous new electronic states. One prominent example is the J_eff =1/2 Mott state in the monolayer iridates, where introducing electrons is predicted to manifest phase behaviors such as high temperature superconductivity analogous to the hole-doped S=1/2 Mott state of the monolayer cuprates. Here we investigate the influence of electron doping on the magnetic ground state of the monolayer spin-orbit assisted Mott material Sr₂IrO₄. By utilizing resonant x-ray scattering our data establish the gradual transition from the long-range antiferromagnetic order intrinsic the unperturbed parent state into to short-range antiferromagnetic state under the light electron substitution. Coincident with the doping threshold where a coherent Fermi surface is established, we observe the formation of a unidirectional spin density wave phase modulated along the Ir-Ir bond diagonal that coexists with a short-range antiferromagnetic background. The potential origins of this phase will be discussed, and our results support the conjecture that the partially quenched Mott phases in electron-doped Sr₂IrO₄ and hole-doped La₂CuO₄ share common competing electronic states.