by A groundbreaking discovery made six years ago sent ripples through the condensed matter physics community: the formation of a superconductor from ultra-thin carbon layers with a slight twist between them. This discovery, known as magic-angle graphene superlattices, paved the way for a new field called twistronics. Yuan Cao, a former MIT graduate student and Harvard Junior Fellow, led the team that made this discovery.
Since then, Cao and his colleagues, including Harvard physicists Amir Yacoby and Eric Mazur, have expanded on this foundational work, making it easier to twist and study various 2D materials. Their latest achievement is a fingernail-sized machine that can twist thin materials at will, eliminating the need to fabricate twisted devices one by one.
2D materials with desirable properties for easy manipulation have significant implications for advanced transistors, optical devices like solar cells, and quantum computers. Controlling the twist angle of these materials is now as simple as controlling their electron density, said Yacoby, Harvard professor of physics and applied physics. Manipulating both density and twist angle opens up a world of possibilities for new discoveries.
Twisted bilayer graphene was first created by Cao as a graduate student in the lab of MIT’s Pablo Jarillo-Herrero. While exciting, the achievement was marred by challenges in replicating the actual twisting. Each twisted device was difficult to produce, making it a time-consuming and unique process. To advance the field, the team envisioned creating a single device to twist multiple layers, eliminating the need for hundreds of unique samples. They call their new device a MEMS (micro-electromechanical system)-based generic actuation platform for 2D materials, or MEGA2D for short.
The Yacoby and Mazur labs collaborated on the design of this new toolkit, which is adaptable to graphene and other materials. By incorporating this new control mechanism via MEGA2D technology, the researchers believe they can resolve many underlying puzzles in twisted graphene and other materials.
In their paper, the researchers demonstrated the utility of their device using two pieces of hexagonal boron nitride, a close relative of graphene. They were able to study the bilayer device’s optical properties, discovering evidence of quasiparticles with coveted topological properties. The ease of their new system opens several scientific avenues, such as employing hexagonal boron nitride twistronics to produce light sources for low-loss optical communication.
The team hopes that their approach will be adopted by other researchers in this thriving field, allowing them to benefit from these new capabilities. Haoning Tang, the paper’s first author and a postdoctoral researcher in Mazur’s lab and a Harvard Quantum Initiative fellow, noted that developing the MEGA2D technology was a long process of trial and error.
“We didn’t know much about how to control the interfaces of 2D materials in real-time, and the existing methods just weren’t sufficient,” Tang said. “After countless hours in the cleanroom and refining the MEMS design—despite many failed attempts—we finally found the working solution after about a year of experiments.” All nanofabrication took place at Harvard’s Center for Nanoscale Systems, where the staff provided invaluable technical support.
The nanofabrication of a device combining MEMS technology with a bilayer structure is a remarkable achievement, said Mazur, the Balkanski Professor of Physics and Applied Physics. The ability to tune the nonlinear response of the resulting device opens the door to a new class of devices in optics and photonics.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
