MIT Physicists Remodel Pencil Lead Into Digital “Gold”

Isolate skinny flakes that may be tuned to exhibit three essential properties.

MIT physicists have metaphorically turned graphite, or pencil lead, into gold by isolating 5 ultrathin flakes stacked in a selected order. The ensuing materials can then be tuned to exhibit three essential properties by no means earlier than seen in pure graphite.

“It’s form of like one-stop purchasing,” says Lengthy Ju, an assistant professor within the MIT Division of Physics and chief of the work, which is reported within the October 5 concern of Nature Nanotechnology. “Nature has loads of surprises. On this case, we by no means realized that each one of those attention-grabbing issues are embedded in graphite.”

Additional, he says, “It is extremely uncommon materials to seek out supplies that may host this many properties.”

The Rise of “Twistronics”

Graphite consists of graphene, which is a single layer of carbon atoms organized in hexagons resembling a honeycomb construction. Graphene, in flip, has been the main focus of intense analysis because it was first remoted about 20 years in the past. Then about 5 years in the past researchers together with a workforce at MIT found that stacking particular person sheets of graphene, and twisting them at a slight angle to one another, can impart new properties to the fabric, from superconductivity to magnetism. The sector of “twistronics” was born.

Within the present work, “we found attention-grabbing properties with no twisting in any respect,” says Ju, who can also be affiliated with the Supplies Analysis Laboratory.

Artist’s rendition of the electron correlation, or means of electrons to speak with one another, that may happen in a particular form of graphite (pencil lead). Credit score: Sampson Wilcox, MIT Analysis Laboratory of Electronics

He and colleagues found that 5 layers of graphene organized in a sure order enable the electrons transferring round inside the fabric to speak with one another. That phenomenon, generally known as electron correlation, “is the magic that makes all of those new properties doable,” Ju says.

Bulk graphite–and even single sheets of graphene–are good electrical conductors, however that’s it. The fabric Ju and colleagues remoted, which they name pentalayer rhombohedral stacked graphene, turns into way more than the sum of its elements.

A Novel Microscope and Its Discoveries

Key to isolating the fabric was a novel microscope Ju constructed at MIT in 2021 that may shortly and comparatively inexpensively decide quite a lot of essential traits of a fabric on the nanoscale. Pentalayer rhombohedral stacked graphene is only some billionths of a meter thick.

Scientists together with Ju had been on the lookout for multilayer graphene that was stacked in a really exact order, generally known as rhombohedral stacking. Says Ju, “there are greater than 10 doable stacking orders whenever you go to 5 layers. Rhombohedral is only one of them.” The microscope Ju constructed, generally known as Scattering-type Scanning Nearfield Optical Microscopy, or s-SNOM, allowed the scientists to establish and isolate solely the pentalayers within the rhombohedral stacking order they had been fascinated with.

Multifaceted Materials Phenomena

From there, the workforce connected electrodes to a tiny sandwich composed of boron nitride “bread” that protects the fragile “meat” of pentalayer rhombohedral stacked graphene. The electrodes allowed them to tune the system with completely different voltages, or quantities of electrical energy. The end result: they found the emergence of three completely different phenomena relying on the variety of electrons flooding the system.

MIT Postdoctoral Affiliate Zhengguang Lu, Assistant Professor Lengthy Ju, and Graduate Pupil Tonghang Han within the lab. The three are authors, with seven others, of a paper in Nature Nanotechnology a couple of particular form of graphite (pencil lead). Credit score: Ju Lab

“We discovered that the fabric could possibly be insulating, magnetic, or topological,” Ju says. The latter is considerably associated to each conductors and insulators. Basically, Ju explains, a topological materials permits the unimpeded motion of electrons across the edges of a fabric, however not via the center. The electrons are touring in a single course alongside a “freeway” on the fringe of the fabric separated by a median that makes up the middle of the fabric. So the sting of a topological materials is an ideal conductor, whereas the middle is an insulator.

“Our work establishes rhombohedral stacked multilayer graphene as a extremely tunable platform to check these new potentialities of strongly correlated and topological physics,” Ju and his coauthors conclude in Nature Nanotechnology.

Reference: “Correlated insulator and Chern insulators in pentalayer rhombohedral-stacked graphene” by Tonghang Han, Zhengguang Lu, Giovanni Scuri, Jiho Sung, Jue Wang, Tianyi Han, Kenji Watanabe, Takashi Taniguchi, Hongkun Park and Lengthy Ju, 5 October 2023, Nature Nanotechnology.
DOI: 10.1038/s41565-023-01520-1

Along with Ju, authors of the paper are Tonghang Han and Zhengguang Lu. Han is a graduate scholar within the Division of Physics; Lu is a postdoctoral affiliate within the Supplies Analysis Laboratory. The 2 are co-first authors of the paper.

Different authors are Giovanni Scuri, Jiho Sung, Jue Wang and Hongkun Park of Harvard College; Kenji Watanabe and Takashi Taniguchi of the Nationwide Institute for Supplies Science in Japan, and Tianyi Han of MIT Physics.

This work was supported by a Sloan Fellowship; the U.S. Nationwide Science Basis; the U.S. Workplace of the Beneath Secretary of Protection for Analysis and Engineering; the Japan Society for the Promotion of Science KAKENHI; the World Premier Worldwide Analysis Initiative of Japan; and the U.S. Air Power Workplace of Scientific Analysis.