Topological Kagome model of moiré charge transfer excitons

Moiré superlattices built from two-dimensional van der Waals materials provide a highly tunable platform for hosting strong electronic correlations and exciton topology. Existing studies of moiré excitons are typically formulated within a hydrogenic model, in which the exciton binding energy dominates the moiré modulation strength. Here we investigate an exceptional regime of moiré charge-transfer (CT) excitons, where the electron and hole are localized at distinct sites of the moiré unit cell. Their spatial separation establishes the exciton real-space orbital as an internal degree of freedom, producing exciton Berry curvature. We show that this enables realization of a Kagome model of moiré CT excitons in a transition-metal dichalcogenide monolayer adjacent to twisted hexagonal boron nitride. The associated exciton Berry curvature gives rise to a topological exciton flat band. This work goes beyond the conventional hydrogenic description of moiré excitons and introduces a promising route toward realizing topological exciton flat bands and bosonic fractional Chern insulators.