Growth of high quality Sr2IrO4 epitaxial thin films on conductive substrates*

Abstract

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.