Nov 15, 2023

(Nanowerk Information) 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.

Key Takeaways

MIT physicists have created a novel type of graphite, which reveals unprecedented properties not present in pure graphite.

This new materials, referred to as pentalayer rhombohedral stacked graphene, is shaped by arranging 5 graphene layers in a selected order with out twisting.

The fabric may be tuned to exhibit insulating, magnetic, or topological properties, providing a variety of functions in electronics and supplies science.

A novel microscope developed at MIT performed a vital position in figuring out and isolating this particular graphene association.

The invention opens new avenues for researching strongly correlated and topological physics, leveraging the tunable nature of this materials.

Artist’s rendition of an electron correlation, or skill of electrons to speak with one another, that may happen in graphene. (Picture: Sampson Wilcox/Analysis Laboratory of Electronics)

The Analysis

“It’s type of like one-stop purchasing,” says Lengthy Ju, an assistant professor within the Division of Physics and chief of the work, which is reported in Nature Nanotechnology (“Correlated insulator and Chern insulators in pentalayer rhombohedral-stacked graphene”). “Nature has loads of surprises. On this case, we by no means realized that every one of those attention-grabbing issues are embedded in graphite.” Additional, he says, “It is vitally uncommon materials to search out supplies that may host this many properties.” 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. Extra not too long ago, 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 sphere of twistronics was born. Within the present work, “we found attention-grabbing properties with no twisting in any respect,” says Ju, who can be affiliated with the Supplies Analysis Laboratory. 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, referred to 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 rather more than the sum of its components.

Novel microscope

Key to isolating the fabric was a novel microscope Ju constructed at MIT in 2021 that may rapidly and comparatively inexpensively decide a wide range of essential traits of a cloth on the nanoscale. Pentalayer rhombohedral stacked graphene is just a few billionths of a meter thick. Scientists together with Ju have been in search of multilayer graphene that was stacked in a really exact order, referred to 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, referred to 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 have been serious about.

Three in a single

From there, the workforce hooked up 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 totally different voltages, or quantities of electrical energy. The consequence: They found the emergence of three totally different phenomena relying on the variety of electrons flooding the system. “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 cloth, however not by way of the center. The electrons are touring in a single route 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 review these new prospects of strongly correlated and topological physics,” Ju and his coauthors conclude.