Strong anisotropy and electronic confinement in 1D quantum-stripe superlattices of iridium oxides*

One-dimensional (1D) systems offer a platform for studying low-dimensional phenomena associated with the onset of critical quantum phase transitions. Here we present a new approach of synthesizing 1D quantum systems by creating dimensionally-confined stripe-superlattices from \textit{in-plane} oriented 2D layered crystals. We have synthesized 1D IrO$_{2}$ stripes using $a$-axis oriented superlattices of Sr$_{2}$IrO$_{4}$ and the wide bandgap insulator LaSrGaO$_{4}$, both of which contain the K$_{2}$NiF$_{4}$ symmetry. The dimensional confinement of our 1D superlattices is confirmed experimentally. Linearly polarized optical spectroscopy shows anisotropic characteristics and one-dimensional electronic confinement of the $J_{eff}_{\, }=$ 1/2 band. Spin and orbital excitations observed in resonant inelastic x-ray scattering suggest enhanced exchange interactions and deconfined orbital excitations in the 1D IrO$_{2}$ stripes. The observed electronic confinement is consistent with density functional theory calculations. The method of transforming layered materials into 1D striped structures is a viable technique for studying dimensional-crossover phase transitions from two- to one-dimension.