Moiré excitons at line defects in transition metal dichalcogenides heterobilayers

In heterobilayers of 2D semiconductors, moiré pattern forms due to the inevitable lattice mismatch and twisting. Earlier works have shown that interlayer excitons in long-period moiré pattern experience a pronounced superlattice potential and have nanoscale patterned light-coupling properties. This leads to remarkable new possibilities to explore exciton physics and tailor optical properties. Line defects such as twin domain boundaries are commonly found in semiconducting transition metal dichalcogenides monolayer, which, in the context of a heterobilayer, leads to an interface between the R-stacking moiré and H-stacking moiré. Here, we show that such interface created by twin-domain boundary realizes a line-defect in the moiré superlattices for interlayer excitons, which localises a one-dimensional exciton mode of topological origin. The defect configuration in the moiré exciton superlattices can be continuously tuned by the interlayer translation and twisting angle, and is also a reflection of the atomic configuration of the domain boundary. The dispersion, wavefunction, and light coupling properties of the interface exciton modes are investigated at different superlattice defect configurations.