Unraveling nodal-line semimetallic phase in SrIrO3 by terahertz quasiparticle dynamics

We demonstrate a rare nonsymmorphic crystalline symmetry-protected nodal-line semimetallic phase in ${\text{SrIrO}}₃$ by acquiring a spatial dependence of the terahertz spectral structure. An extremely low momentum-relaxation scattering rate of $\ensuremath{\sim}8.32 {\text{cm}}^{\ensuremath{-}1}$ emerging from high-mobility Dirac electrons, diversity in the carrier dynamics controlled by the orientation and symmetry of epitaxial thin films, and a group theory analysis corroborate the formation of this phase. The presence of Dirac electrons only along selected crystal orientations of this three-dimensional semimetal uniquely interrelates the symmetry-enforced band crossings, a template that can explore the prevalence of this superior topological phase in complex systems.