Suppression of weak ferromagnetism in ultra-thin iridates by interfacial engineering of octahedral rotations*

The 5d transition metal oxide Sr₂IrO₄ has been predicted to be a new type of high-Tc superconductor upon electron doping, and exhibits many behaviors similar to cuprates. However, no direct evidences (zero resistance and Meissner effects) of superconductivity have been observed up to date. A major difference between irdates and cuprates is the sizable IrO₆ octahedral rotations and weak ferromagnetic ordering (considerable net magnetic moments) in the IrO₂ plane, which may hinder the formation of cooper pairing. To suppress the IrO₆ octahedral rotations, we grew epitaxial SrIrO₃ films on cubic SrTiO₃ substrate by reactive molecular-beam epitaxy. Via the interfacial clamping effect imposed by substrates, low-energy electron diffraction (LEED) measurements exhibit no octahedral rotations in 2 and 1 unit-cell SrIrO₃ films. In-situ angle-resolved photoemission spectroscopy (ARPES) and first principle calculations suggest an intriguing antiferromagnetic ground state with no canted magnetic moments in these ultra-thin SrIrO₃ films. Our work provides a new path to explore superconductivity in iridates.