Synthesis and Electrical Transport Study of Complex Iridates grown using Solid-Source Metal-Organic MBE

Complex iridium-based oxides form an intriguing class of materials where the experimental synthesis challenges have greatly impeded the realization of the rich quantum mechanical phase-space; predictions of which have ranged from topological semimetals to axion insulators. Sr₂IrO₄ is one such candidate material that has been predicted to be an unconventional high T_c superconductor but has lacked direct experimental evidence. This can be primarily attributed to the synthesis challenges associated with Ir, which has ultra-low vapor pressure and low oxidation potential making high-quality thin film synthesis using ultra-high vacuum techniques like Molecular Beam Epitaxy (MBE) extremely challenging. In this work, we report on the MBE synthesis of Sr₂IrO₄ thin films using Ir(acac)_3, a solid metal-organic precursor which allows Ir supply at temperatures less than 200 ^oC, as opposed to more than 2000 ^oC required for a pure Ir metal source. We further demonstrate a spontaneous segregation of any unoxidized Ir to the film surface leaving behind nominally phase pure Sr₂IrO₄ thin films, which we use to study the temperature dependent magneto transport properties as a function of rare-earth doping. We’ll also further discuss strategies to make these thin films more metallic and possibly superconducting.