Structural evolution and electronic properties of (Sr1−xCax)2−yIrO4+z spin-orbit-assisted insulators

Due to their unique balance of energy scales, correlated iridates have proven a fruitful materials platform for both the prediction and discovery of numerous novel electronic phases and ground states. The comparable strengths of spin-orbit coupling, on-site Coulomb interactions, and local crystal-field splitting inherent to the iridium cations hosted within various lattice geometries has led to the realization of a novel form of spin-orbit assisted Mott insulating ground state, where the iridium's spin and orbital angular momenta become entangled into a ${J}_{\mathbf{\text{eff}}}$=1/2 wave function. In this paper, the stability of this state with respect to chemical pressure is explored in the prototypical spin-orbit assisted Mott insulator Sr2IrO${}₄$. This study reveals that isovalent substitution of smaller Ca${}²⁺$ onto Sr${}²⁺$ sites in this system drives the lattice to evolve through three distinct structural phases with increasing Ca${}²⁺$ content: evolving from the parent quasi-two-dimensional $n$=1 Ruddlesden-Popper structure, to a novel three dimensional corner sharing IrO${}₆$ octahedral network to a quasi-one dimensional IrO${}₆$ edge-sharing chain structure. All three phases remain insulators reliant on the inherently strong spin-orbit coupling of Ir. However, their magnetic properties evolve dramatically across the phase diagram. The work here provides a global view of the evolution of the structural and electronic properties of Sr2IrO${}₄$ as its lattice is destabilized via chemical pressure.