A discovery six years ago took the condensed-matter physics world by storm: Ultra-thin carbon stacked in two barely askew layers became a superconductor, and changing the twist angle between layers could toggle their electrical properties. The landmark 2018 paper describing “magic-angle graphene superlattices” launched a brand new field called “twistronics,” and the primary writer was then-MIT graduate student and up to date Harvard Junior Fellow Yuan Cao.
Along with Harvard physicists Amir Yacoby, Eric Mazur, and others, Cao and colleagues have built on that foundational work, smoothing a path for more twistronics science by inventing a better strategy to twist and study many kinds of materials.
A brand new paper in Nature describes the team’s fingernail-sized machine that may twist thin materials at will, replacing the necessity to fabricate twisted devices one after the other. Thin, 2D materials with properties that will be studied and manipulated easily have immense implications for higher-performance transistors, optical devices akin to solar cells, and quantum computers, amongst other things.
“This development makes twisting as easy as controlling the electron density of 2D materials,” said Yacoby, Harvard professor of physics and applied physics. “Controlling density has been the first knob for locating recent phases of matter in low-dimensional matter, and now, we will control each density and twist angle, opening infinite possibilities for discovery.”
Cao first made twisted bilayer graphene as a graduate student within the lab of MIT’s Pablo Jarillo-Herrero. Exciting because it was, the achievement was tempered by challenges with replicating the actual twisting.
On the time, each twisted device was hard to provide, and because of this, unique and time-consuming, Cao explained. To do science with these devices, they needed tens and even a whole bunch of them. They wondered if they might make “one device to twist all of them,” Cao said — a micromachine that might twist two layers of fabric at will, eliminating the necessity for a whole bunch of unique samples. They call their recent device a MEMS (micro-electromechanical system)-based generic actuation platform for 2D materials, or MEGA2D for brief.
The Yacoby and Mazur labs collaborated on the design of this recent tool kit, which is generalizable to graphene and other materials.
“By having this recent ‘knob’ via our MEGA2D technology, we envision that many underlying puzzles in twisted graphene and other materials may very well be resolved in a breeze,” said Cao, now an assistant professor at University of California Berkeley. “It should actually also bring other recent discoveries along the way in which.”
Within the paper, the researchers demonstrated the utility of their device with two pieces of hexagonal boron nitride, a detailed relative of graphene. They were in a position to study the bilayer device’s optical properties, finding evidence of quasiparticles with coveted topological properties.
The convenience of their recent system opens several scientific roadways, for instance, employing hexagonal boron nitride twistronics to provide light sources that will be used for low-loss optical communication.
“We hope that our approach will likely be adopted by many other researchers on this prosperous field, and all can profit from these recent capabilities,” Cao said.
The paper’s first writer is nanoscience and optics expert Haoning Tang, a postdoctoral researcher in Mazur’s lab and a Harvard Quantum Initiative fellow, who noted that developing the MEGA2D technology was an extended strategy of trial and error.
“We didn’t know much about methods to control the interfaces of 2D materials in real time, and the present methods just weren’t cutting it,” she said. “After spending countless hours within the cleanroom and refining the MEMS design — despite many failed attempts — we finally found the working solution after a couple of yr of experiments.” All nanofabrication took place at Harvard’s Center for Nanoscale Systems, where staff provided invaluable technical support, Tang added.
“The nanofabrication of a tool combining MEMS technology with a bilayer structure is a veritable tour de force,” said Mazur, the Balkanski Professor of Physics and Applied Physics. “Having the ability to tune the nonlinear response of the resulting device opens the door to a complete recent class of devices in optics and photonics.”
