Growth of high quality Sr₂IrO₄ epitaxial thin films onconductive substrates

Ruddlesden-Popper iridium oxides have attracted considerable interest because of the many proposed novel quantum states that arise from the large spin-orbit coupling of the heavy iridium atoms in them. A prominent example is the single layer Sr₂IrO₄, in which superconductivity has been proposed under electron doping. However, the synthesis of Sr₂IrO₄ high quality thin films has been a huge challenge due to the easy formation of impurities associated with different numbers of SrO layers. Thus techniques to optimize the growth of pure phase Sr₂IrO₄ are urgently required. Here we report the deposition of high quality Sr₂IrO₄ thin films on both insulating SrTiO₃ and conducting SrTiO₃:Nb substrates using pulsed laser deposition assisted with reflective high-energy electron diffraction. The optimal deposition temperature of Sr₂IrO₄ epitaxial films on SrTiO₃:Nb substrates is about 90 °C lower than that on SrTiO₃ substrates. The electrical transports of high quality Sr₂IrO₄ films are measured, which follow the three-dimensional Mott variable-range hopping model. The film magnetizations are measured, which show weak ferromagnetism below~240 K with a saturation magnetization of~0.2 μ_B/Ir at 5 K. This study provides applicable methods to prepare high quality 5d Sr₂IrO₄ epitaxial films, which could be extended to other Ruddlesden-Popper phases and potentially help the future study of exotic quantum phenomena in them.