Moiré Excitons in WS₂-MoSe₂ Heterobilayers

Twisted van der Waals (vdW) heterostructures exhibit periodic variations, leading to a new type of in-plane superlattice known as moiré superlattice/pattern which modifies considerably the optical properties of excitons in transition metal dichalcogenides (TMD) vdW heterostructures. Here, we report on optical and magneto-optical properties of WS₂/MoSe₂heterobilayers with twist angles around 0° and 60° under out-plane magnetic fields up to 20 T [1]. We observed two neutral exciton peaks in the PL spectra: the lower energy one exhibits a reduced g-factor relative to that of the higher energy peak, and much lower than the recently reported values for interlayer excitons in other vdW heterostructures such as WSe₂-MoSe₂. In addition, similar values of g-factors are obtained for samples with twist angles of approximately 0° and 60° which indicates a weak hybridization between the intralayer and interlayer excitons for this heterostructure. Furthermore, time resolved PL experiments reveal that the lifetimes of the moiré exciton emission peaks are much shorter (&lt; 50 ps) than the values reported in the literature for the interlayer excitons in other TMD heterostructures (≈ 2 ns), which also indicates a weak exciton hybridization. The observed reduction of the g-factor value for the moiré exciton was explained by the quantized center-of-mass momentum of the moiré-confined exciton resulting in a exciton momenta value away from the exciton band edge. In general, our experimental and theoretical results provide evidence that such a discernible g-factor stems from the spatial confinement of the exciton in the potential landscape created by the moiré pattern, due to lattice mismatch and/or inter-layer twist in heterobilayers [1].<br/>References<br/>[1] Y. Galvão Gobato et al, Nano Letters 22, 8641 (2022)