A discovery six years in the past took the condensed-matter physics world by storm: Extremely-thin carbon stacked in two barely askew layers grew to become a superconductor, and altering the twist angle between layers may toggle their electrical properties. The landmark 2018 paper describing “magic-angle graphene superlattices” launched a brand new area referred to as “twistronics,” and the primary writer was then-MIT graduate scholar and up to date Harvard Junior Fellow Yuan Cao.
Along with Harvard physicists Amir Yacoby, Eric Mazur, and others, Cao and colleagues have constructed on that foundational work, smoothing a path for extra twistronics science by inventing a neater method to twist and research many forms of supplies.
A brand new paper in Nature describes the workforce’s fingernail-sized machine that may twist skinny supplies at will, changing the necessity to fabricate twisted units one after the other. Skinny, 2D supplies with properties that may be studied and manipulated simply have immense implications for higher-performance transistors, optical units comparable to photo voltaic cells, and quantum computer systems, amongst different issues.
“This improvement makes twisting as straightforward as controlling the electron density of 2D supplies,” mentioned Yacoby, Harvard professor of physics and utilized physics. “Controlling density has been the first knob for locating new phases of matter in low-dimensional matter, and now, we are able to management each density and twist angle, opening limitless prospects for discovery.”
Cao first made twisted bilayer graphene as a graduate scholar within the lab of MIT’s Pablo Jarillo-Herrero. Thrilling because it was, the achievement was tempered by challenges with replicating the precise twisting.
On the time, every twisted gadget was laborious to provide, and because of this, distinctive and time-consuming, Cao defined. To do science with these units, they wanted tens and even a whole bunch of them. They puzzled if they may make “one gadget to twist all of them,” Cao mentioned — a micromachine that would twist two layers of fabric at will, eliminating the necessity for a whole bunch of distinctive samples. They name their new gadget a MEMS (micro-electromechanical system)-based generic actuation platform for 2D supplies, or MEGA2D for brief.
The Yacoby and Mazur labs collaborated on the design of this new device equipment, which is generalizable to graphene and different supplies.
“By having this new ‘knob’ by way of our MEGA2D expertise, we envision that many underlying puzzles in twisted graphene and different supplies may very well be resolved in a breeze,” mentioned Cao, now an assistant professor at College of California Berkeley. “It can definitely additionally carry different new discoveries alongside the best way.”
Within the paper, the researchers demonstrated the utility of their gadget with two items of hexagonal boron nitride, a detailed relative of graphene. They had been in a position to research the bilayer gadget’s optical properties, discovering proof of quasiparticles with coveted topological properties.
The convenience of their new system opens a number of scientific roadways, for instance, using hexagonal boron nitride twistronics to provide gentle sources that can be utilized for low-loss optical communication.
“We hope that our strategy can be adopted by many different researchers on this affluent area, and all can profit from these new capabilities,” Cao mentioned.
The paper’s first writer is nanoscience and optics skilled Haoning Tang, a postdoctoral researcher in Mazur’s lab and a Harvard Quantum Initiative fellow, who famous that growing the MEGA2D expertise was an extended means of trial and error.
“We did not know a lot about the right way to management the interfaces of 2D supplies in actual time, and the prevailing strategies simply weren’t chopping it,” she mentioned. “After spending numerous hours within the cleanroom and refining the MEMS design — regardless of many failed makes an attempt — we lastly discovered the working answer after a few yr of experiments.” All nanofabrication happened at Harvard’s Middle for Nanoscale Programs, the place employees supplied invaluable technical assist, Tang added.
“The nanofabrication of a tool combining MEMS expertise with a bilayer construction is a veritable tour de pressure,” mentioned Mazur, the Balkanski Professor of Physics and Utilized Physics. “Having the ability to tune the nonlinear response of the ensuing gadget opens the door to an entire new class of units in optics and photonics.”