By using a combination of heteroepitaxial growth, structure refinement based on synchrotron x-ray diffraction and first-principles calculations, we show that the symmetry-protected Dirac line nodes in the topological semimetallic perovskite SrIrO3 ca
n be lifted simply by applying epitaxial constraints. In particular, the Dirac gap opens without breaking the Pbnm mirror symmetry. In virtue of a symmetry-breaking analysis, we demonstrate that the original symmetry protection is related to the n-glide operation, which can be selectively broken by different heteroepitaxial structures. This symmetry protection renders the nodal line a nonsymmorphic Dirac semimetallic state. The results highlight the vital role of crystal symmetry in spin-orbit-coupled correlated oxides and provide a foundation for experimental realization of topological insulators in iridate-based heterostructures.
Relativistic current induced torques and devices utilizing antiferromagnets have been independently considered as two promising new directions in spintronics research. Here we report electrical measurements of the torques in structures comprising a $
sim1$~nm thick layer of an antiferromagnet IrMn. The reduced Neel temperature and the thickness comparable to the spin-diffusion length allow us to investigate the role of the antiferromagnetic order in the ultra-thin IrMn films in the observed torques. In a Ta/IrMn/CoFeB structure, IrMn in the high-temperature phase diminishes the torque in the CoFeB ferromagnet. At low temperatures, the antidamping torque in CoFeB flips sign as compared to the reference Ta/CoFeB structure, suggesting that IrMn in the antiferromagnetic phase governs the net torque acting on the ferromagnet. At low temperatures, current induced torque signatures are observed also in a Ta/IrMn structure comprising no ferromagnetic layer.
