Doping driven structural distortion in the bilayer iridate (Sr${}_{1-x}$La${}_x$)${}_3$Ir${}_2$O${}_7$

Abstract

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${}_x$)${}_3$Ir${}_2$O${}_7$ with $x=0.035$ and $x=0.071$. Once electrons are introduced into the bilayer spin-orbit assisted Mott insulator Sr${}_3$Ir${}_2$O${}_7$, 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 $P{2}_1/c$ 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.

8 pages, 4 figures