Researchers Unveil New Method to Control Exciton Flow in Moiré Superlattices

A team of researchers from Carnegie Mellon University, UC Riverside, and other institutions has made significant strides in controlling the flow of excitons within moiré superlattices. This innovative approach, detailed in a paper published in Nature Communications on December 21, 2025, showcases how correlated electrons can be leveraged to enhance exciton transport in layered materials.

Excitons, which are pairs of bound negatively charged electrons and positively charged holes, are vital for energy transport in semiconductors. These pairs also appear in transition metal dichalcogenides—thin materials made of a transition metal and two chalcogen atoms. The study explores how stacking two such layers with a slight rotational mismatch creates a moiré superlattice that can influence exciton dynamics.

Innovative Techniques in Moiré Superlattices

The research team, led by Sufei Shi, senior author of the study, focused on the WS₂/WSe₂ system to investigate quantum phenomena arising from strong interactions between electrons and excitons. “Even back in 2021, we discovered the strong electron-electron interaction, which inspired us to manipulate exciton dynamics,” Shi explained.

To create the moiré superlattice, the researchers precisely stacked transition metal dichalcogenide layers at specific angles. By employing optical techniques, they prompted exciton formation between these layers. The team then adjusted the density of electrons within the superlattice to measure how far and quickly excitons could travel, a property known as diffusivity.

The findings revealed that when the density of electrons reached a threshold sufficient to form a Mott insulator state, the diffusivity of excitons was enhanced by an astonishing factor of up to 100. Conversely, in conditions where electrons organized into a rigid, crystal-like structure, referred to as Wigner crystal states, the exciton flow was significantly suppressed.

Implications for Quantum Devices and Optoelectronics

This breakthrough presents a new methodology for improving exciton diffusivity in transition metal dichalcogenide-based moiré superlattices. Shi noted that the potential applications extend to engineering specific excitonic states in future quantum and optoelectronic devices. “With the robust exciton in 2D semiconductors, there is a growing interest in utilizing excitons as information carriers instead of electrons,” he stated.

One challenge has been that excitons are charge-neutral and do not respond easily to electric fields, unlike electrons. The team’s ability to modulate exciton diffusivity through the interactions of correlated electrons represents a significant advancement in the field. Future research may build on these findings, exploring ways to further manipulate exciton flow using electric fields or nanoscale device patterns.

Shi emphasized the importance of this work: “We are also interested in how exciton-exciton interactions can be harnessed to manipulate exciton diffusion.” The ongoing research aims to deepen understanding of interlayer exciton diffusivity and its experimental modulation, paving the way for innovative technologies based on moiré superlattices.

As the field evolves, insights from this study could inspire new avenues for research and technology development, expanding the applications of excitons in electronic devices.