Charge-conserving creation and annihilation of topological phase singularities in atomically thin semiconductors

Overview & Synopsis

Atomically thin transition metal dichalcogenides provide a promising material platform for optical phase manipulation, as rapid variations in their dielectric functions can give rise to topological phase singularities (PSs). However, PS evolution while preserving topological charge conservation has not yet been investigated in exciton enabled PS systems. Here, using atomically thin MoS2 films on sapphire as a model system, we theoretically and experimentally demonstrate that the evolution of dielectric dispersion determines the creation, trajectory, merging, and annihilation of optical PSs under topological charge conservation. By varying the MoS2 film thickness, we experimentally realize this evolution through the gradual shrinking of the high energy n-k dispersion loop, which modifies its intersection with the zero reflection condition. Our results provide a general strategy for exploring and manipulating topological optical states.