LAUSR

Neutron single-crystal diffraction and rotational anisotropy optical second harmonic generation data are presented resolving the nature of the structural distortion realized in electron-doped (Sr_(1−x)La_x)_3Ir_2O_7 with x = 0.035 and x = 0.071. Once electrons are introduced into the bilayer spin-orbit assisted Mott insulator Sr_2Ir_2O_7, previous studies have identified the appearance of a low-temperature structural distortion and have suggested the presence of a competing electronic instability in the phase diagram of this material. Our measurements resolve a lowering of the structural symmetry from monoclinic C2/c to monoclinic P2_1/c and the creation of two unique Ir sites within the chemical unit cell as the lattice distorts below a critical temperature T_S. Details regarding the modifications to oxygen octahedral rotations and tilting through the transition are discussed as well as the evolution of the low-temperature distorted lattice as a function of carrier substitution.