Quantum Confining Excitons with an Electrostatic Moiré Superlattice

Quantum confining excitons has been a persistent challenge in the pursuit of strong exciton interactions and quantum light generation. Unlike electrons, which can be readily controlled via electric fields, imposing strong nanoscale potentials on excitons to enable quantum confinement has proven challenging. In this Letter, we utilize piezoelectric force microscopy to image the domain structures of twisted hexagonal boron nitride (h-BN), revealing evidence of strong in-plane electric fields at the domain boundaries. By placing a monolayer MoSe_{2} only 1 to 2 nm away from the twisted h-BN interface, we observe energy splitting of neutral excitons and Fermi polarons by several millielectronvolts at the moiré domain boundaries. We attribute such observations to excitons confined in a nanoscale one-dimensional electrostatic potential created by the strong in-plane electric fields at the moiré domain boundaries. Intriguingly, this 1D quantum confinement results in pronounced polarization anisotropy in the excitons' reflection and emission, persistent to temperatures as high as ∼80  K. These findings open new avenues for exploring and controlling strongly interacting excitons for classical and quantum optoelectronics.