Interlayer exciton diffusion in a WS2/WSe2 moiré superlattice with tunable electrostatic doping. Credit: Nature Communications (2025). DOI: 10.1038/s41467-025-65602-5

Excitons are pairs of bound negatively charged electrons and positively charged holes that form in semiconductors, enabling the transport of energy in electronic devices. These pairs of charge carriers also emerge in transition metal dichalcogenides, thin semiconducting materials comprised of a transition metal and two chalcogen atoms.

Researchers at Carnegie Mellon University, UC Riverside, and other institutes have introduced a new strategy to control the flow of energy in structures comprised of two transition metal dichalcogenide layers stacked with a small rotational mismatch, also known as moiré superlattices.

Their proposed approach, introduced in a paper published in Nature Communications, entails the active tuning of electronic states in moiré superlattices in ways that alter the transport of excitons.

"Over the past few years, we have been working on the WS2/WSe2 to study quantum many-body phenomena arising from strong electron-electron and exciton-exciton interactions," Sufei Shi, senior author of the paper, told Phys.org.

"Even back in 2021, when we discovered the strong electron-electron interaction, we found that the interlayer excitons were interacting strongly with correlated electrons, which inspired us to use this electron-exciton interaction to manipulate exciton dynamics."

Credit: Yan et al.

Leveraging correlated electrons in moiré superlattices

As part of their study, Shi and his colleagues fabricated transition metal dichalcogenide layers and then stacked them at a specific angle to create a moiré superlattice. They then used optical techniques to prompt the formation of excitons between the two layers.

The researchers modulated the density of electrons in their system and collected measurements to assess how far and quickly excitons spread, a measure known as diffusivity. Finally, they compared the flow of excitons in different electronic phases.

"We controlled the exciton diffusivity in our system by electrostatic doping (gate voltage), which controls how many electrons are in the moiré superlattices," explained Shi. "These electrons are highly interacting with each other and are so-called correlated electrons. Once the electrons form in the Mott insulator, the exciton diffusivity is greatly modified."

Notably, Shi and his colleagues found that when electrons in their moiré superlattice were dense enough to produce a so-called Mott insulator state, the flow (i.e., diffusivity) of excitons in the system was enhanced by up to 100 times.

In contrast, they found that exciton diffusivity was suppressed in situations in which electrons are organized into a very rigid, crystal-like pattern, producing so-called Wigner crystal states.

New routes to develop quantum devices and optoelectronics

This recent work introduces a promising approach to enhance exciton diffusivity in transition metal dichalcogenide-based moiré superlattices. This strategy could soon be used to engineer desired excitonic states in quantum and optoelectronic devices.

"With the robust exciton in 2D semiconductors, it has been widely proposed to use excitons for possible devices, which use excitons rather than electrons as information carriers," said Shi.

"However, there is an intrinsic problem, namely that the exciton is charge neutral and cannot be controlled easily with an electric field, like the electrons. By utilizing the interaction between correlated electrons and excitons, we have achieved the electrically tunable exciton diffusivity."

In the future, other research teams could build on the team’s findings to develop new technologies based on moiré superlattices, modulating the flow of excitons through these devices to prompt the emergence of desired physical states. In addition, the results gathered by Shi and his colleagues could inspire further fundamental physics studies investigating the physical underpinnings of interlayer exciton diffusivity and how it can be altered experimentally.

"We will now further explore how to control exciton diffusivity via electric field, or nanoscale device pattern," added Shi.

"We are also interested in exploring how exciton-exciton interaction can be used to further manipulate the exciton diffusion. Finally, we plan to investigate how to employ the gained understanding to further construct new correlated exciton states."

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More information: Li Yan et al, Anomalously enhanced diffusivity of moiré excitons via manipulating the interplay with correlated electrons, Nature Communications (2025). DOI: 10.1038/s41467-025-65602-5.

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Citation: Controlling exciton flow in moiré superlattices: New method leverages correlated electrons (2025, December 21) retrieved 21 December 2025 from https://phys.org/news/2025-12-exciton-moir-superlattices-method-leverages.html

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