Unveiling the Atomic Twist: A Dance of Light and Matter
Imagine a world where atoms, the building blocks of our universe, perform an intricate dance, twisting and untwiring in perfect harmony. This fascinating phenomenon, occurring at a pace far beyond our perception, has been unveiled by a groundbreaking collaboration between Cornell and Stanford University researchers.
The Atomic Choreography
In a crystalline sheet, mere atoms thick, a pulse of light sets the stage. Atoms, usually static, begin to move in a coordinated rhythm, like dancers interpreting a complex beat. This atomic choreography, a result of precisely timed energy bursts, unfolds in a trillionth of a second, making it invisible to the human eye and traditional scientific tools.
Capturing the Unseen
To witness this hidden dance, researchers employed ultrafast electron diffraction, a technique akin to filming matter at its fastest timescales. Using a specialized instrument and a high-speed detector, both developed at Cornell, the team captured the dynamic twisting motion of atomically thin materials in response to light.
Unveiling Moiré Materials
The findings, published in Nature, open new avenues for understanding and controlling the behavior of moiré materials. These stacked 2D structures possess unusual properties that can be fine-tuned simply by twisting one layer atop another. The research provides insights into how light can be harnessed to manipulate materials in real time, with potential applications in superconductivity, magnetism, and quantum electronics.
A Dynamic Twist
Professor Jared Maxson, a co-author of the study, explains, "People have known that stacking and twisting atomically thin layers can change a material's behavior. What's new is that we can enhance this twist dynamically with light and observe it in real time."
Previously, researchers believed that once moiré materials were stacked at a fixed angle, the structure remained static. However, this study reveals a dynamic twist. Co-author Fang Liu, project lead at Stanford, created the moiré materials and stated, "The atoms inside each moiré unit cell perform a circle dance. It's not fixed at all; the atoms move."
The Ultrafast Electron Diffraction Technique
To capture this fleeting dance, researchers used an ultrafast electron diffraction instrument, firing intense electron bursts at a sample after a laser pulse. This pump-and-probe method reveals atomic shifts over time. The key to success was Cornell's Electron Microscope Pixel Array Detector (EMPAD), a highly sensitive detector that essentially became a hypersensitive movie camera for atoms.
A Powerful Collaboration
The collaboration between Cornell and Stanford combined materials understanding with electron-beam expertise. Liu's lab at Stanford provided the specially engineered materials, while Cornell built the tools and carried out the experiment. Maxson emphasized, "There's no way we could have witnessed this phenomenon without combining these two fields of expertise."
The data analysis and reconstruction of atomic motion were led by Cameron Duncan, a Ph.D. graduate from Maxson's group. Duncan's contributions were crucial in capturing the ultrafast moiré signal.
Future Prospects
Liu's lab has already produced new moiré samples to push the limits of Cornell's ultrafast instrument. The teams plan to explore how different materials and twist angles respond to light, deepening their understanding of actively controlling quantum behavior in real time.
The measurements were conducted at Cornell's Newman Lab, with contributions from the Center for Bright Beams and the Cornell Laboratory for Accelerator-Based Sciences and Education. The project involved students and faculty from various disciplines, including physics, applied physics, engineering physics, and accelerator science.
The EMPAD detector was developed by Cornell researchers David Muller and Sol Gruner, with support from the Department of Energy, the National Science Foundation, and the Defense Advanced Research Projects Agency.
This groundbreaking research opens a new chapter in our understanding of atomic behavior and its potential applications. It invites further exploration and discussion on the fascinating interplay between light and matter.
