Two-dimensional orbital Hall insulators

Detailed analyses of the spin and orbital conductivities are performed for different topological phases of certain classes of two-dimensional multiorbital materials. Our calculations show the existence of orbital-Hall effect (OHE) in topological insulators, with values that exceed those obtained for the spin-Hall effect (SHE). Notably, we have found nontopological insulating phases that exhibit OHE in the absence of SHE. We demonstrate that the OHE in these systems is deeply linked to exotic momentum-space orbital textures that are triggered by an intrinsic Dresselhaus-type interaction that arises from a combination of orbital attributes and lattice symmetry. Our results strongly indicate that other classes of systems with nontrivial orbital textures and/or orbital magnetism may also exhibit large OHE even in their normal insulating phases.