Researchers at Carnegie Mellon University and UC Riverside, alongside other institutions, have developed a groundbreaking method to control the flow of excitons in moiré superlattices. Their findings, published in the journal Nature Communications, reveal a novel approach to manipulating energy transport in semiconductor structures formed by stacking layers of transition metal dichalcogenides.
Excitons, which consist of pairs of bound electrons and holes, play a crucial role in energy transport within electronic devices. These excitons form in materials composed of a transition metal and chalcogen atoms, including graphene-like structures known as transition metal dichalcogenides. The new strategy proposed by the researchers focuses on adjusting electronic states within these moiré superlattices, leading to significant alterations in exciton transport.
Innovative Method to Manipulate Exciton Dynamics
The research team, led by Sufei Shi, has been studying the interactions between excitons and correlated electrons in the WS2/WSe2 system. “We have focused on the quantum many-body phenomena that arise from strong electron-electron and exciton-exciton interactions,” Shi explained. Their earlier work highlighted strong electron interactions, which motivated them to explore how these dynamics could be harnessed to influence exciton behavior.
In their experiments, the researchers fabricated layers of transition metal dichalcogenides and stacked them at a specific angle to create the desired moiré superlattices. They employed optical techniques to generate excitons and manipulated the density of electrons within the system. By measuring the diffusivity of the excitons, they assessed how far and quickly these energy carriers spread through the material.
The team discovered that controlling exciton diffusivity was feasible through electrostatic doping—applying a gate voltage to adjust the electron density in the moiré superlattice. Shi noted that the presence of correlated electrons significantly modified exciton dynamics. “When we achieved a Mott insulator state, the diffusivity of excitons increased by up to 100 times,” Shi stated. Conversely, when electrons formed a rigid, crystal-like arrangement, known as Wigner crystal states, exciton diffusivity was suppressed.
Implications for Quantum Devices and Optoelectronics
The findings present a promising avenue for enhancing exciton diffusivity in semiconductor-based moiré superlattices. This technique could pave the way for innovative quantum and optoelectronic devices that utilize excitons as information carriers, a shift from traditional electron-based systems. Shi emphasized the challenges posed by excitons, which are charge neutral and difficult to control with electric fields. By leveraging the interaction between correlated electrons and excitons, the researchers achieved electrically tunable exciton diffusivity.
Looking ahead, Shi and his team anticipate that other research groups will build upon their work to develop new technologies based on moiré superlattices. The ability to modulate exciton flow could facilitate the emergence of desired physical states in these advanced materials. Furthermore, their results may inspire deeper investigations into the fundamental physics governing interlayer exciton diffusivity and its experimental manipulation.
“We will explore methods to control exciton diffusivity via electric fields or nanoscale device patterns,” Shi added. The team is also keen to investigate how exciton-exciton interactions might further influence exciton diffusion and explore the potential for constructing new correlated exciton states.
This research signifies a substantial step forward in the understanding and application of excitons in modern materials, with implications that could reshape the landscape of quantum and optoelectronic technologies.
