麻豆淫院

A few years ago, physicists were surprised to learn that two atomically thin layers of an electronic material like graphene creates a pattern that changes the material's properties and can even turn it into a superconductor. This superimposed grid, like what would emerge if two window screens were laid slightly askew, is called a moir茅 pattern.

But why stop there? It turns out adding a third layer, with each layer twisted at slightly different angles, produces even more complex interferences known as supermoir茅 patterns (aka moir茅 of moir茅). The supermoir茅 pattern induces profound changes in how electrons move through the material, but until recently, scientists had had trouble measuring exactly what changes occur and why.

Now, applied physicists in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have used a specially designed microscope to probe the properties of supermoir茅 patterns in trilayer graphene to an extent that was never possible before. Using their microscope, they saw many new states of matter in which electrons would get stuck or form unusual groups, leading to changes in the entire system's electronic behavior and opening doors to studying layered materials with precisely controllable properties.

Published in Science, the was co-led by former Harvard Quantum Initiative Prize postdoctoral fellow Yonglong Xie and former SEAS graduate student Andrew Pierce, who worked in the lab of Amir Yacoby, the Mallinckrodt Professor of 麻豆淫院ics and Applied 麻豆淫院ics.

The ultra-long supermoir茅 patterns visible in twisted trilayer materials had been considered by some to be imperfections of little consequence amidst the simpler moir茅 structures that emerge when only two layers are present. The new Harvard paper challenges that assumption and introduces the concept of supermoir茅 engineering鈥攈ow that additional pattern-on-pattern could be used as a probe to uncover the overall properties of these special materials. The supermoir茅 pattern is relatively large and can be easily controlled, introducing potential for designing exotic new materials for thin electronics and other applications.

"Going into this study, if you asked me if I thought the supermoir茅 was good for anything, I probably would've said it'll just be a nuisance," said Pierce, now a postdoctoral researcher at Cornell. "But it turned out to give us new information about the system鈥攊nformation that would've been hard to get with other techniques besides ours."

Understanding of supermoir茅 patterns had been limited by the fact that the patterns can vary significantly across different regions in a sample. To solve this problem, the researchers used their single-electron transistor microscope, developed in Yacoby's lab at SEAS, that is capable of examining materials with spatial resolution of about 100 nanometers and is sensitive to perturbations in individual electrons. A sharp needle with a sensor at its tip scans the sample and captures these details.

The microscope allowed the team to detect very slight changes in moir茅 and supermoir茅 patterns in two- and three-layer graphene, and the resulting electronic properties per pixel. By analyzing the correlations between these quantities, they gleaned new insights into how the supermoir茅 patterns in particular influence the entire system.

"This additional long-range pattern that until now was largely overlooked could be used as a probe to understand the material properties of the parent material," said Xie, now an assistant professor at Rice University.

The results could enhance understanding of quantum phenomena, including the lossless conduction of electrons known as superconductivity, and lead to next-generation materials that contain multiple tunable properties.