Seminar: Confining Excitons in a Moiré Potential

Excitons—bound states of electrons and holes analogous to hydrogen atoms—play a central role in the optical properties of semiconductors. In two-dimensional materials, reduced dielectric screening enhances their binding energies to hundreds of meV, making them a natural platform to explore strong correlation effects.

In moiré systems, the interplay between lattice mismatch and twist-induced band reconstruction modifies the excitonic spectrum, enabling phenomena such as topological exciton bands. A direct consequence is the emergence of a moiré potential that can localize excitons, in contrast to their typically delocalized nature in conventional semiconductors.

In this seminar, I will provide a pedagogical review of excitons in 2D and moiré materials. I then present recent work [1], where we introduce a technique based on photocurrent atomic force microscopy that combines spatial and energy resolution to image excitons with nanometer precision at room temperature. We directly observe exciton confinement in twisted MoS₂ without relying on unit-cell averaging or cryogenic conditions. The observed excitonic levels are well captured by an effective continuum model.

[1] Laurens J. M. Westenberg et al., arXiv:2511.20398.