Obstruction-Driven Parity Inversion for Enhanced Optical Absorption in Hexagonal Transition Metal Dichalcogenides

Abstract: The optical selection rule states that opposite parity between the valence and conduction bands is required for optical absorption to occur. However, monolayer hexagonal transition metal dichalcogenides (h-TMDs) such as $ \mathrm{MoS}_{2} $ exhibit pronounced optical absorption despite their nominally dipole-forbidden d-d transitions. In this Letter, we elucidate a parity inversion mechanism through which obstruction-driven band inversion promotes dipole-allowed optical transitions near the band edge in monolayer h-TMDs. By comparing trivial and obstructed atomic limit phases, we show that intersite interactions between hybridized d orbitals induce parity inversion. Our results provide a novel approach to tuning optical properties through parity control, bridging the gap between topology and light-matter interaction.