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 Ba3TiIr2O9 hosts a Dirac nodal line (DNL) along the A-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-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 (approximate to 300 h/e Omega(-1) cm(-1)). This suggests the possible application of the material as a spin current detector.