Emergent topological mirror insulator in t2g -orbital systems

Motivated by the itinerant band structure of high-Tc iron pnictides, which exhibit four Dirac cones in the bulk, we demonstrate the prospect of pnictides with transition elements to be topological insulators in two dimensions. In this report, we explore interaction-induced topological phases, in contrast to the spin-orbit-coupling interaction, as the crucial mechanism for tuning Dirac metals into Z2-topological insulators protected by time reversal and mirror symmetries. We find spontaneous orbital currents generated through nearest-neighbor interorbital Coulomb interaction in the t2g manifold of the d orbitals. When spin degrees of freedom are incorporated, spontaneous orbital currents lead to two stable topological phases of the ground state. The first topological insulator is an anomalous orbital Hall phase, characterized by an even Chern number, while the second topological insulator is realized by protected mirror symmetries with a Z2 index.