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| Fang Liu, assistant professor of chemistry in Stanford’s School of Humanities and Sciences Photo Credit: Fawn Hallenbeck/Stanford University |
A study led by Stanford and Cornell researchers shows how light could be used to control the behavior of moiré materials, atomically thin layers that gain unusual properties when stacked and offset. The research has implications for developing superconductivity, magnetism, and quantum electronics.
A pulse of light sets the tempo in the material. Atoms in a crystalline sheet just a few atoms thick begin to move—not randomly, but in a coordinated rhythm, twisting and untwisting in sync like dancers following a beat.
Until now, researchers hadn’t been able to directly observe how those layers physically respond to a burst of light. In a recent study, a team led by Stanford and Cornell University researchers showed that the atomic layers can briefly twist more tightly together, then spring back, like a coiled ribbon releasing its energy.
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| A model of moiré materials: stacked two-dimensional structures that create unusual patterns when one layer is rotated over the other. When made with atomically thin layers, moiré materials exhibit quantum properties including superconductivity, a way to very efficiently conduct electricity without energy loss. The model pictured here was designed and 3D-printed by Greg Zaborski Jr., a Stanford graduate student in materials science and engineering. Video Credit: Fawn Hallenbeck/Stanford University |
Their findings, published in Nature, open new possibilities for understanding and controlling the behavior of moiré materials—stacked 2D structures whose unusual properties can be tuned simply by twisting one layer slightly atop another. The results provide insight into how light might one day be used to manipulate materials in real time, with implications for future technologies in superconductivity, magnetism, and quantum electronics.
“Previously, researchers thought that once you stack these moiré materials at a fixed angle, the whole structure is fixed,” said co-corresponding author Fang Liu, assistant professor of chemistry in Stanford’s School of Humanities and Sciences, who created the moiré materials for this research. “What we have shown is that it is definitely not fixed at all—the atoms will move. In fact, the atoms inside each moiré unit cell will do a kind of circle dance.”
This atomic choreography, set in motion by precisely timed bursts of energy, happens far too fast for the human eye or even traditional scientific tools to detect. The entire sequence plays out in about a trillionth of a second.
To witness it, the researchers turned to ultrafast electron diffraction, a technique capable of filming matter at very fast timescales. Using a Cornell-built instrument and high-speed detector, the team captured atomically thin materials responding to light with a dynamic twisting motion.
“People have long known that by stacking and twisting these atomically thin layers, you can change how a material behaves. You can turn it into a superconductor or make electrons act in strange new ways,” said Jared Maxson, Cornell professor of physics and co-corresponding author on the paper. “What’s new here is that we enhance that twist dynamically with light and actually watch it happen in real time."
To capture this fleeting dance, researchers used the ultrafast electron diffraction instrument. Built and refined in Maxson’s lab, it fires intense bursts of electrons at a sample just after it has been struck by a laser pulse. This pump-and-probe method reveals how the atoms shift over time.
While Cornell built the tools and carried out the experiment, the specially engineered materials used in the study came from Liu’s lab at Stanford.
“There’s no way we could have witnessed this phenomenon without combining materials understanding with experimental understanding,” Maxson said. “We could build the best machine in the world, but without the right materials and the expertise to make them, it wouldn’t happen. That’s what made this collaboration with Fang Liu’s group so powerful.”
Liu also felt that the collaboration was key to the project’s success.
“Jared Maxson’s ultrafast instrument is the only one that could actually see the moiré pattern, and his team even modified it in real time to make the experiment possible. This was a true collaboration.”
For future work, Liu’s lab has already produced a new set of moiré samples designed to push the limits of Cornell’s ultrafast instrument. The teams are planning the next round of experiments to see how different materials and twist angles respond to light, work that could deepen their understanding of how to actively control quantum behavior in real time.
Published in journal: Nature
Title: Photoinduced twist and untwist of moiré superlattices
Authors: Cameron J. R. Duncan, Amalya C. Johnson, Indrajit Maity, Angel Rubio, Matthew Gordon, Adam C. Bartnik, Michael Kaemingk, William H. Li, Matthew B. Andorf, Chad A. Pennington, Ivan V. Bazarov, Mark W. Tate, David A. Muller, Julia Thom-Levy, Sol. M. Gruner, Aaron M. Lindenberg, Jared M. Maxson, and Fang Liu
Source/Credit: Stanford University (adapted from a Cornell University press release)
Reference Number: phy111325_02
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