Scientists at MIT have discovered remarkable characteristics in graphite by precisely aligning five layers of graphene. This configuration, known as pentalayer rhombohedral stacked graphene, can display insulating, magnetic, or topological traits, which constitutes a notable advancement in the field of materials physics facilitated by state-of-the-art nanoscale microscopy.
This new structure allows for the isolation of thin layers with the capability to demonstrate three distinct and important attributes.
Physicists at MIT have essentially turned pencil lead into a form that resembles “gold” by carefully extracting five ultra-thin graphene layers and arranging them in a distinct sequence. This engineered material reveals three distinctive characteristics not previously observed in natural graphite.
“This is akin to a one-stop shop,” asserts Long Ju, Assistant Professor at MIT’s Department of Physics and the project’s lead researcher, as reported in the October 5 issue of Nature Nanotechnology. “There are numerous unexpected phenomena in nature. In this instance, we had not anticipated discovering all these intriguing qualities within graphite.”
Additionally, he remarks, “It is quite unusual to find materials that can accommodate this variety of properties.”
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Emergence of “Twistronics”
Graphite is composed of layers of graphene, a single-atom-thick carbon structure that forms a honeycomb-like pattern. The intensive investigation of graphene commenced about two decades ago when it was first isolated. Then, approximately five years ago, MIT researchers, among others, found that by stacking layers of graphene and applying a small twist between them, new properties could be endowed upon the material, ranging from superconductivity to magnetism, hence the origin of the field known as “twistronics”.
In their most recent research, Ju notes, “We found intriguing properties without any twisting,” Ju is also associated with the Materials Research Laboratory.
An artist’s depiction accompanies the discussion, illustrating the electron correlation in a special form of graphite, as detailed by Sampson Wilcox of MIT’s Research Laboratory of Electronics.
Ju and his team discovered that a certain arrangement of five graphene layers enables electrons within the material to interact, a process termed electron correlation. “This interaction is the key to unlocking these novel properties,” states Ju.
While bulk graphite and even individual graphene sheets conduct electricity effectively, the material isolated by Ju and his team, known as pentalayer rhombohedral stacked graphene, is far more complex.
A Breakthrough Microscope and Its Discoveries
The isolation of this material became possible thanks to an innovative microscope developed by Ju in 2021 at MIT, designed to identify a range of critical material characteristics at the nanoscale efficiently and cost-effectively. Pentalayer rhombohedral stacked graphene measures just a few nanometers in thickness.
The search was for multilayer graphene with a highly specific stacking pattern, rhombohedral stacking. “With up to five layers, there are over ten potential stacking sequences. Rhombohedral is merely one possibility,” Ju explains. The Scattering-type Scanning Nearfield Optical Microscopy (s-SNOM) that Ju constructed enabled the team to pinpoint and isolate the pentalayers with the desired rhombohedral arrangement.
Complex Material Behaviors
Subsequently, the researchers applied electrodes to a minuscule assembly sandwiched between boron nitride layers, which preserved the delicate core of pentalayer rhombohedral stacked graphene. The electrodes allowed for the manipulation of the material with varying electrical voltages, leading to the discovery of three distinct phenomena based on the electron concentration within the system.
The MIT team, including Postdoctoral Associate Zhengguang Lu, Assistant Professor Long Ju, and Graduate Student Tonghang Han, who are among the authors of the Nature Nanotechnology publication, found the material could assume insulating, magnetic, or topological states. A topological state means electrons flow freely around the material’s edge but not through its center, creating a sort of conductive path along the material’s boundary with an insulating interior.
In conclusion, their research identifies rhombohedral stacked multilayer graphene as an exceptionally adjustable platform for exploring the novel realms of strongly correlated and topological physics, as stated in Nature Nanotechnology.
The paper credits additional authors: Graduate Student Tonghang Han and Postdoctoral Associate Zhengguang Lu of MIT, who are the co-first authors, along with Giovanni Scuri, Jiho Sung, Jue Wang, and Hongkun Park from Harvard University; Kenji Watanabe and Takashi Taniguchi from Japan’s National Institute for Materials Science, and Tianyi Han of MIT Physics.
This research received support from a Sloan Fellowship, the U.S. National Science Foundation, the U.S. Office of the Under Secretary of Defense for Research and Engineering, the Japan Society for the Promotion of Science KAKENHI, the World Premier International Research Initiative of Japan, and the U.S. Air Force Office of Scientific Research.
Frequently Asked Questions (FAQs) about nanoscale graphene properties
What is the significance of the MIT physicists’ discovery with graphite?
The MIT physicists’ discovery is significant because they have managed to engineer graphite in such a way that it exhibits unique insulating, magnetic, and topological properties. This paves the way for advancements in materials physics and has applications in various technological innovations.
How does pentalayer rhombohedral stacked graphene differ from regular graphite?
Pentalayer rhombohedral stacked graphene is a specially engineered form of graphite that is composed of five layers of graphene stacked in a precise sequence. This configuration allows for electron correlation within the material, enabling it to display insulating, magnetic, or topological characteristics, which are not found in natural graphite.
What is “twistronics,” and how does it relate to this research?
“Twistronics” is a field of study that involves stacking two-dimensional layers of materials like graphene and introducing a slight twist between them to create new electronic properties. This research relates to twistronics in that it involves the manipulation of graphene layers, but without the twisting aspect, revealing new properties through different means of layering and electron interaction.
What makes the microscope developed by MIT’s Long Ju innovative?
The microscope developed by Ju, known as Scattering-type Scanning Nearfield Optical Microscopy (s-SNOM), is innovative because it enables researchers to identify and analyze the properties of materials like the pentalayer rhombohedral stacked graphene at the nanoscale efficiently and cost-effectively, which is critical for advancing research in nanotechnology and materials science.
Who contributed to the research on pentalayer rhombohedral stacked graphene?
The research was a collaborative effort, with contributions from Long Ju, Zhengguang Lu, and Tonghang Han of MIT, along with other researchers from Harvard University and the National Institute for Materials Science in Japan. The project was part of a broader initiative supported by various institutions including the Sloan Fellowship and the U.S. National Science Foundation.
More about nanoscale graphene properties
- MIT Department of Physics
- Nature Nanotechnology Journal
- Materials Research Laboratory at MIT
- Scattering-type Scanning Nearfield Optical Microscopy (s-SNOM)
- U.S. National Science Foundation
- Japan Society for the Promotion of Science KAKENHI
- World Premier International Research Center Initiative (WPI), Japan
- U.S. Air Force Office of Scientific Research
- Sloan Research Fellowships
