Researchers Discover New Uses for Moiré Superlattices

An international group of researchers has used moiré superlattices to answer theoretical questions in physics, which could lead to future developments in quantum computing. 

"The fact that we can manipulate excitons with strong interactions with each other is a big advantage," said Sufei Shi, associate professor of physics at Carnegie Mellon University. "It would allow us to construct quantum states of excitons that are different from those arising from interacting electrons."

Previously, physicists have demonstrated that electrons can form crystal structures under specific circumstances. They theorized the same crystal structures could be formed by excitons, a form of electrons elevated to a higher energy state by light.

Shi and colleagues overlaid a monolayer of tungsten disulfide (WS2) on a monolayer of tungsten diselenide (WSe2) to create a moiré superlattice, an overlapping periodic pattern of crystals that can influence election motion. The researchers found that excitons can form the same kinds of crystal structures electrons do. The superlattice also allows the excitons to interact with electrons and each other.

Yongtao Cui, associate professor of physics and astronomy at the University of California, Riverside, said that the moiré superlattices could be a breakthrough for physicists studying excitons.

"Excitons are short-lived states with neutral electric charge, so they are typically hard to control," Cui said. "The use of Moiré superlattices can now provide a power means to achieve that."

Besides finding that the superlattice can control excitons, Shi said that the superlattice can be used to help solve theoretical physics problems with experimental means.

For example, a Hamiltonian interaction known as the bosonic Hubbard model, which describes how subatomic particles interact in a lattice, is extremely difficult to simulate. The model can grow complex very quickly, to the point where even supercomputers could take an infinitely long time to finish the simulation.

Using a moiré superlattice with the proper conditions, Shi said physicists can now work with the bosonic Hubbard model experimentally, removing the necessity for computational modeling.

"We can just run the experiment and see the results," Shi said. "It's a lot easier, and it's robust because the experiment is tolerant to a single defect."

Shi said that the next steps in the research involve investigating how excitons can be manipulated and what their functions are. He said that if they can increase the lifetime of excitons, it could open up a potential future for quantum computing.

Shi and Cui were joined by Zhen Lian, Yuze Meng, Lei Ma, Indrajit Maity, Li Yan, Qiran Wu, Xiong Huang, Dongxue Che, Xiaotong Chen, Xinyue Chen, Mark Blei, Takashi Taniguchi, Kenji Wantanabe, Sefaattin Tongay and Johannes Lischener on the project, "Valley-Polarized Excitonic Mott Insulator in WS2/WSe2 Moiré Superlattice." The project was funded by the National Science Foundation.