Dirac nodal lines and large spin Hall effect in the 6H -perovskite iridate Ba3TiIr2O9

Nodal line semimetals with symmetry protected band structure offer a platform for the investigation of a number of emerging quantum phenomena. Using first-principles calculation combined with symmetry analysis, we show that ${\mathrm{Ba}}_{3}{\mathrm{TiIr}}_{2}{\mathrm{O}}_{9}$ hosts a Dirac nodal line (DNL) along the $A\text{\ensuremath{-}}L$ direction of the Brillouin zone, protected by the glide reflection symmetry. In the presence of the spin-orbit coupling, even though the DNL along the $A\text{\ensuremath{-}}L$ direction is protected, DNLs along other directions as well as multiple nodal loops present in the system gap out. The gapped out Dirac nodal loops act as a source of spin Berry curvature, resulting in a large spin Hall conductivity ($\ensuremath{\approx}300$ $\frac{\ensuremath{\hbar}}{e}\phantom{\rule{4pt}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}{\phantom{\rule{0.16em}{0ex}}\mathrm{cm}}^{\ensuremath{-}1}$). This suggests the possible application of the material as a spin current detector.