Observation of orbital angular momentum from ultrathin topological insulator metasurface

Orbital angular momentum (OAM) existing in the vortex light beam with isolated singularities and spiral phase distribution presents significant applications in optical communications and light-field manipulation. The generation of OAM based on plasmonic metasurfaces is generally limited by the large optical loss and weak tunability of metal materials. Three-dimensional (3D) topological insulators (TIs) with insulating bulk states and topologically protected surface states allow the excitation of surface plasmons with low loss in the high-frequency region. Herein, we designed and fabricated an ultrathin Sb