Photoexcitation flips 2D moiré devices from metals to insulators in ultrafast test

June 4, 2026 feature Photoexcitation flips 2D moiré devices from metals to insulators in ultrafast test Ingrid Fadelli Author Sadie Harley Scientific Editor Robert Egan Associate Editor Quantum materials, materials with properties that are governed by the laws of quantum mechanics describing many-body interactions, have proved promising for the development of various advanced technologies. Many of these materials undergo so-called phase transitions, switching between different physical states that alter how electrons flow through them. Some previous studies have demonstrated the transition from insulating states to metallic states in quantum materials, via a process called photoexcitation (i.e., the excitation of electrons using light). Yet the opposite transition, from metallic to insulating states, has so far proved difficult to realize using light alone. Researchers at Columbia University, in collaboration with UC Riverside, recently demonstrated an ultrafast photo-induced metal-to-insulator transition in two-dimensional (2D) moiré heterostructures, quantum materials consisting of 2D layers stacked on top of each other, with a slight misalignment between them. Their paper, published in Physical Review Letters, could open new exciting avenues for the development of quantum technologies and ultra-fast optical devices. "Our lab has been developing pump-probe spectroscopy to provide a time-domain view of moiré quantum matter," Xiaoyang Zhu, senior author of the paper, told Phys.org. "In careful analysis of this process, we realized that the commonly used graphite electrode for electrostatic gating may provide additional functions, since most excitation energy is absorbed by the graphite electrodes. The current work is a result of such a surprising function." The realization of a photo-induced metal-to-insulator transition As part of their study, Zhu and his colleagues fabricated moiré devices comprised of stacked ultra-thin layers of tungsten disulfide (WS₂) and tungsten diselenide (WSe₂). They also included graphite gates via which they could inject electrical charge into the devices. The researchers then used short laser pulses to light up the material. Initially, they doped each device into a metallic state, which means that electrons could move freely through them. Soon after they excited the material with the laser pulses, however, the devices transitioned into correlated insulating states. "In the photoexcitation of charge-doped moiré quantum matter, pump excitation results in the disruption of a correlation, as is observed for the photo-induced insulator to metal transition (IMT), with characteristic spectroscopic signatures," explained Zhu. "The present paper results from a serendipitous discovery. At high pump powers, we made the astonishing observation of a spectroscopic signature for the reverse process, i.e., a metal-to-insulator transition." The team performed various analyses to better understand the physical underpinnings of the photo-induced phase transition they observed. These analyses revealed that the mechanism responsible for this transition was the ultrafast injection of photoexcited holes from the graphite electrode. A promising route for developing ultrafast quantum devices This study introduces a promising strategy to enable ultrafast transitions in quantum devices based on moiré materials. In the future, it could open new opportunities for the development of cutting-edge quantum devices, including ultrafast quantum memories and quantum processors. "Our findings provide an effective means to control carrier density in moiré quantum phases on ultrafast time scales," said Zhu. "This paper should also be considered a methodology foundation for future studies of van der Waals structures with ultrafast laser pulses." The researchers hope that their recent work will pave the way for further studies aimed at realizing rapid phase transitions in quantum devices. Meanwhile, they plan to explore the potential of their approach for tuning quantum phases in moiré devices in advantageous ways. "We now want to take advantage of this discovery to control various moiré quantum phases on ultrafast time scales and to explore potentially hidden quantum phases," added Zhu. Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Yiliu Li et al, Photoinduced Metal-to-Insulator Transitions in 2D Moiré Devices, Physical Review Letters (2026). DOI: 10.1103/mt2s-jkbl. On arXiv: DOI: 10.48550/arxiv.2510.21005 Journal information: Physical Review Letters , arXiv Key concepts Electronic structureMesoscopicsOptical & microwave phenomenaOptics & lasersPhase transitions2-dimensional systemsQuantum many-body systemsStrongly correlated systemsOptical techniques© 2026 Science X Network