Electrical Switching of Optical Responses in Atomic Monolayers

Due to the 2D character and reduced screening, optical responses in atomic monolayers are dominated by robust excitons, bound electron–hole pairs, with binding energies orders of magnitude larger than those of bulk materials. Although group‐V elemental monolayers have attracted significant interest due to their nontrivial topological properties, the evolution of their optical responses across topological phase transitions remains largely unexplored. By combining a low‐energy effective Hamiltonian and the Bethe–Salpeter equation to accurately describe the Coulomb interaction, we reveal the effect of an electric field on the band structure and absorption spectra. We show that an electric field induces two distinct types of band crossings in monolayer SbH, both of which universally invert the helicity of excitonic absorption despite their distinct origins. Our findings pave the way for experimental detection of topological changes through optical probing with circularly polarized light.