Phase transformation and hole doping in iridate thin films by controlled oxygen annealing*

In an effort to metallize Ir-based perovskites through hole doping, we anneal epitaxially-grown thin films of Sr₂IrO₄ at controlled oxygen pressures. The post-annealed films show a drop in room-temperature resistivity of up to 3 orders of magnitude, and an evolution from insulating to semimetallic behavior. Scanning transmission electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy reveal a structural transformation to a novel pseudocubic phase, increasing with annealing time, pressure, and reduced film thickness. The evolution towards metallicity is attributed to the phase transformation, interstitial oxygens, and Ir vacancies. We discuss the prospects of achieving hole-doped superconductivity in this spin-orbit semimetal.