Unidirectional spin density wave state in metallic (Sr 1− x La x ) 2 IrO 4

Materials that exhibit both strong spin–orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the J eff = 1/2 Mott state in Sr 2 IrO 4 , where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S = 1/2 Mott state of La 2 CuO 4 . While bulk superconductivity currently remains elusive, anomalous quasiparticle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d -wave gap are observed upon electron-doping Sr 2 IrO 4 . Here we establish a magnetic parallel between electron-doped Sr 2 IrO 4 and hole-doped La 2 CuO 4 by unveiling a spin density wave state in electron-doped Sr 2 IrO 4 . Our magnetic resonant X-ray scattering data reveal the presence of an incommensurate magnetic state reminiscent of the diagonal spin density wave state observed in the monolayer cuprate (La 1− x Sr x ) 2 CuO 4 . This link supports the conjecture that the quenched Mott phases in electron-doped Sr 2 IrO 4 and hole-doped La 2 CuO 4 support common competing electronic phases.