New Method Enhances Exciton Flow in Moiré Superlattices

Researchers from Carnegie Mellon University and the University of California, Riverside, have developed a groundbreaking method to control the flow of excitons in moiré superlattices. This innovative technique, detailed in a study published in Nature Communications on December 21, 2025, leverages correlated electrons to enhance energy transport in electronic devices.

Excitons, which are pairs of negatively charged electrons and positively charged holes, play a crucial role in energy transport within semiconductors. These charge carriers also form in transition metal dichalcogenides, a class of materials consisting of a transition metal and two chalcogen atoms. The research team focused on structures comprising two layers of these materials, stacked with a slight rotational mismatch to create what are known as moiré superlattices.

Controlling Exciton Dynamics Through Electron Interactions

The researchers explored the effects of electron interactions within these moiré superlattices. Senior author Sufei Shi highlighted their previous work with WS2 and WSe2, which involved studying quantum many-body phenomena stemming from strong electron-electron and exciton-exciton interactions. This foundational research inspired the current study, where the team aimed to manipulate exciton dynamics through the strong interactions between electrons and excitons.

To create their moiré superlattices, the researchers fabricated layers of transition metal dichalcogenides and stacked them at a precise angle. They then employed optical techniques to induce the formation of excitons between the layers. By adjusting the density of electrons in the system using electrostatic doping, the team was able to examine how excitons spread, known as their diffusivity.

By controlling the number of electrons present, the researchers discovered significant variations in exciton flow. “We controlled the exciton diffusivity in our system by adjusting the gate voltage, which dictates the electron density in the moiré superlattices,” Shi explained. Notably, the study found that when the electron density reached levels sufficient to create a Mott insulator state, the flow of excitons increased by as much as 100 times. Conversely, exciton diffusivity decreased when electrons formed a rigid, crystal-like arrangement, referred to as Wigner crystal states.

Implications for Quantum Devices and Optoelectronics

This research opens new avenues for enhancing exciton diffusivity in transition metal dichalcogenide-based moiré superlattices, with potential applications in quantum and optoelectronic devices. Shi noted the significance of this work, stating, “With the robust exciton in 2D semiconductors, it has been proposed to use excitons as information carriers instead of electrons.” The challenge had been that excitons are charge neutral and not easily manipulated by electric fields. However, by harnessing the interaction between correlated electrons and excitons, the team achieved an electrically tunable exciton diffusivity.

Future research could build on these findings to further refine technologies based on moiré superlattices. By modulating exciton flow through these devices, researchers could induce desired physical states. Shi expressed interest in exploring additional methods to control exciton diffusivity, including the use of electric fields or nanoscale device patterns. The team also aims to investigate how exciton-exciton interactions can further manipulate diffusion processes and contribute to the development of new correlated exciton states.

The study represents a significant step forward in understanding the interplay between excitons and correlated electrons, potentially paving the way for innovative applications in advanced electronic and optoelectronic systems.