Real-Space Imaging of Moir\'e-Confined Excitons in Twisted Bilayer MoS$_2$

TL;DR

This study used room-temperature photocurrent atomic force microscopy to directly image and resolve site-specific exciton confinement within a twisted bilayer MoS$_2$ moiré pattern at nanometre resolution, advancing understanding of moiré excitons.

Contribution

It provides the first direct real-space imaging of moiré-confined excitons in twisted bilayer MoS$_2$, revealing site-specific localization and validating a Wannier-based exciton model.

Findings

Direct imaging of excitons at nanometre scale

Site-specific localization of direct and indirect excitons

Validation of a Wannier-based moiré exciton model

Abstract

Twisted two-dimensional semiconductors generate a moir\'e landscape that confines excitons (bound electron-hole pairs) into programmable lattices, offering routes to efficient light sources, sensing, and room-temperature information processing. However, direct real-space imaging of confined excitonic species within a moir\'e unit cell remains challenging; existing claims are inferred from spatially averaged far-field signals that are intrinsically insufficient to resolve nanometre-scale variations. Here, we imaged excitons across the moir\'e of a 2$^{\circ}$ twisted bilayer MoS$_2$ with nanometre resolution using room-temperature photocurrent atomic force microscopy. We directly resolved site-selective confinement: direct and indirect excitons localize at different stacking registries of the moir\'e, with contrast governed by alignment between site-selective generation and confinement minima. A Wannier-based moir\'e-exciton model reproduces the measured energies and the moir\'e-induced localization of the exciton wavefunction. These species-specific, unit-cell-resolved measurements constrain microscopic models of moir\'e excitons, provide benchmarks for excitonic order, and establish a device-compatible route to engineering excitonic lattices in van der Waals heterostructures.