Antiferromagnetic ground state and evidence for the spin nematic order in single layer SrIrO₃ film.

Spin-orbit coupling (SOC) plays a pivotal role in generating nontrivial topologies that underpin remarkable quantum phenomena such as unconventional superconductivity. The 5d perovskite-structured iridates, which are representative materials with strong SOC exhibit a variety of quantum phases depending on dimensionality, for example, from SOC-induced Mott insulators to Dirac semimetals. Here, we present the antiferromagnetic ground state characterized by electronic band structure in a single unit cell SrIrO₃ (SIO) film by angle-resoled photoemission spectroscopy (ARPES) and dynamical mean field theory (DMFT) calculations. Unlike the paramagnetic metallic state of 3D bulk SIO, a single unit cell of SIO could have the antiferromagnetic phase because it is analogous to the single-layer Sr₂IrO₄ compound. Thanks to the strain effect from a substrate, one can also induce metallicity in a single-unit cell SIO. Furthermore, a peculiar split band structure reveals the presence of spin nematic order, as expected in Sr₂IrO₄. Linear polarization dependence as well as circular dichroism experiments on our samples allows us to confirm the spin nematic ground state. Our results spectroscopically demonstrate the quantum order believed to be associated with high-temperature superconductivity in strongly SOC-driven materials with controlled dimensionality.