Unveiling the Atomic Dance: How Light Twists and Turns Atomic Layers
Imagine a world where light becomes the conductor, orchestrating an intricate dance of atoms. In a groundbreaking discovery, researchers have revealed a fascinating phenomenon where a simple pulse of light sets off a synchronized rhythm within atomic layers. These atoms, arranged in a crystalline sheet just a few atoms thick, twist and untwist in perfect harmony, resembling dancers moving to the beat.
But here's where it gets controversial... This atomic choreography, occurring at an astonishingly fast pace, has long eluded detection by traditional scientific tools. The entire sequence unfolds in approximately a trillionth of a second, making it virtually invisible to the human eye. To capture this elusive dance, a collaborative effort between Cornell and Stanford University researchers turned to a cutting-edge technique known as ultrafast electron diffraction.
Using a specialized instrument and a high-speed detector, both developed at Cornell, the team successfully filmed matter at its fastest timescales. Their findings, recently published in Nature, open up exciting new avenues for understanding and manipulating the behavior of moiré materials - stacked 2D structures with unique properties that can be fine-tuned by a simple twist.
"The ability to stack and twist atomically thin layers has been known to change material behavior, even turning them into superconductors or making electrons behave in bizarre ways," explained Jared Maxson, a professor of physics at Cornell and co-corresponding author of the study. "What's groundbreaking here is that we've enhanced this twist dynamically with light, and actually witnessed it in real time."
Until now, researchers had been unable to directly observe the physical response of these layers to a burst of light. However, this study revealed that the atomic layers can momentarily twist more tightly together, only to spring back, akin to a coiled ribbon releasing its stored energy.
"Contrary to previous beliefs, the structure of moiré materials is not fixed once stacked at a specific angle," said Fang Liu, co-corresponding author and project lead at Stanford. "Our research shows that the atoms within each moiré unit cell perform a unique circle dance."
To capture this fleeting dance, the researchers utilized the ultrafast electron diffraction instrument, refined in Maxson's lab. This instrument fires intense bursts of electrons at a sample immediately after it's been exposed to a laser pulse, revealing how atoms shift over time through a pump-and-probe method.
A critical component of the experiment's success was the Electron Microscope Pixel Array Detector (EMPAD), a high-speed, ultra-sensitive detector developed at Cornell. Originally designed for still images, the EMPAD was repurposed as a hypersensitive movie camera for atoms, capturing incredibly subtle features that could have easily been lost in the noise.
"Combining our understanding of materials with electron-beam expertise was crucial," Maxson emphasized. "Without the right materials and the know-how to create them, this phenomenon would have remained hidden."
Liu added, "Jared's ultrafast instrument was the key to visualizing the moiré pattern, and his team even modified it in real time to make the experiment feasible. This collaboration was a true meeting of minds."
The data analysis and reconstruction of atomic motion from complex diffraction patterns were led by Cameron Duncan, a Ph.D. graduate from Maxson's group. Duncan's contributions were instrumental in successfully detecting the ultrafast moiré signal.
For future research, Liu's lab has already produced a new set of moiré samples designed to push the boundaries of Cornell's ultrafast instrument. The teams are planning further experiments to explore how different materials and twist angles respond to light, aiming to deepen their understanding of actively controlling quantum behavior in real time.
This groundbreaking research was carried out at Cornell's Newman Lab, with contributions from the Center for Bright Beams and the Cornell Laboratory for Accelerator-Based Sciences and Education. It involved a diverse range of students and faculty across physics, applied and engineering physics, and accelerator science.
The EMPAD detector, a cornerstone of this research, was developed by Cornell researchers David Muller, the Samuel B. Eckert Professor of Engineering, and Sol Gruner, professor emeritus of physics. The work was supported by the Department of Energy, the National Science Foundation, and the Defense Advanced Research Projects Agency.
As we delve deeper into the world of atomic dance, the question arises: Could this discovery revolutionize our understanding of materials and pave the way for groundbreaking technologies in superconductivity, magnetism, and quantum electronics? The answers lie in the intricate twists and turns of atomic layers, illuminated by the power of light.
