Optically-Controlled Orbitronics on a Triangular Lattice*

Orbital polarization of a Bloch state in a crystal can endow a band structure with nontrivial geometry and manifest itself in unique responses to applied fields. We study this for an on-site orbital multiplet on a 2D primitive triangular lattice where orbital degeneracies are lifted by propagation on a Bravais lattice. The model contains fully orbitally-derived band structure degeneracies including a line-node required by the perpendicular mirror symmetry and two types of point degeneracies protected by PT symmetry. Crucially, and in contrast to the well-studied analogous problem on the honeycomb lattice, here point degeneracies with opposite winding numbers are generically offset in energy which enables the activation of anomalous transport responses using readily-implemented spatially-uniform local potentials. We demonstrate this by calculation of an anomalous charge Hall effect activated by coherently coupling to a circularly polarized optical field and an orbital Hall effect describing an orbital angular momentum current directed perpendicular to an applied in plane electric field.