Symmetry-enforced topological Dirac semimetal for giant spin-orbit torque with ultralow power dissipation.

Current-driven spin-orbit torque (SOT) enables electrical control of magnetization for next-generation memory and logic, but reducing switching current and power consumption is still a major challenge. Topological semimetals provide an attractive platform because they combine metallic conductivity with topological states that can efficiently generate spin currents. However, while most studied systems rely on accidental band inversions, the SOT response of symmetry-enforced Dirac semimetals remains largely unexplored. Here, we demonstrate that the non-symmorphic symmetry-enforced Dirac semimetal hexagonal SrIrO3 exhibits record-high SOT efficiency. In situ angle-resolved photoemission spectroscopy on high-quality epitaxial thin films directly confirmed the topological Dirac semimetal state, revealing bulk Dirac points near the Fermi level and spin-momentum locked surface states. Leveraging these synergistic features, we achieve a very high SOT efficiency of 2.26 and a substantial spin Hall conductivity of 0.96 × 105 ([Formula: see text]- /2e) Ω-1 m-1, enabling perpendicular magnetization switching at an exceptionally low current density of 5.9 × 105 A/cm2. Our findings establish symmetry-enforced topological semimetals as a robust materials platform for achieving superior charge-spin conversion, opening a pathway toward ultra-low-power spintronic devices.