Quantum mechanics

Materials science

Fine structure

Moiré pattern

Semiconductor

Photon

Physics

Exciton

Optics

Molecular physics

Condensed matter physics

Heterojunction

Electron

Optoelectronics

Nature

Interlayer excitons (ILXs) — electron–hole pairs bound across two atomically thin layered semiconductors — have emerged as attractive platforms to study exciton condensation1–4, single-photon emission and other quantum information applications5–7. Yet, despite extensive optical spectroscopic investigations8–12, critical information about their size, valley configuration and the influence of the moiré potential remains unknown. Here, in a WSe2/MoS2 heterostructure, we captured images of the time-resolved and momentum-resolved distribution of both of the particles that bind to form the ILX: the electron and the hole. We thereby obtain a direct measurement of both the ILX diameter of around 5.2 nm, comparable with the moiré-unit-cell length of 6.1 nm, and the localization of its centre of mass. Surprisingly, this large ILX is found pinned to a region of only 1.8 nm diameter within the moiré cell, smaller than the size of the exciton itself. This high degree of localization of the ILX is backed by Bethe–Salpeter equation calculations and demonstrates that the ILX can be localized within small moiré unit cells. Unlike large moiré cells, these are uniform over large regions, allowing the formation of extended arrays of localized excitations for quantum technology. Imaging the electron and hole that bind to form interlayer excitons in a 2D moiré material enables direct measurement of its diameter and indicates&nbsp;the localization of its centre of mass.

Structure of the moiré exciton captured by imaging its electron and hole