Gateway to 3D Material Revolution: Researchers have put a graphene twist on graphite

A team led by the University of Washington has discovered that by stacking a sheet of graphene on top of bulk graphite with a small twist angle (top), exotic properties present at the graphene-graphite interface (yellow) can penetrate the graphite itself. Credit: Ellis Thompson

A groundbreaking study of the University of Washington demonstrated that graphite, a 3D material, can be manipulated to possess properties of its 2D counterpart, graphene. This paves the way for the potential modification of other bulk materials to exhibit 2D-like properties, potentially expanding the frontier of technological innovations.

Explore the potential of 2D materials

For many years, scientists have explored the potential of two-dimensional materials, made up of a single layer of atoms, to revolutionize various fields such as computing, communication and energy. Within these materials, subatomic particles such as electrons can only move in two dimensions, leading to unusual electron behavior and so-called exotic properties. These include bizarre forms of magnetism, superconductivity, and other collective behaviors among electrons that could all be useful in computing, communication, energy, and other fields.

Traditionally, researchers have assumed that these exotic 2D properties exist only in single-layered sheets or short stacks, with so-called bulk versions of these materials exhibiting different behaviors due to their complex 3D atomic structures.

An unexpected twist on 2D materials

Contrary to the above assumption, a groundbreaking study published on July 19 at Nature by a team led by the University of Washington has shown that it is possible to endow graphite, a loose 3D material found in everyday pencils, with similar properties to its 2D counterpart, graphene. Not only was this breakthrough unexpected, but the team also believes its approach could be used to test whether similar types of bulk materials can also take on similar 2D properties. If so, 2D sheets won’t be the only source for scientists to fuel technological revolutions. In bulk, 3D materials could be just as useful.

Stacking a single layer on a single layer or two layers on two layers has been the goal to unlock new physics in 2D materials for several years now. In these experimental approaches, this is where many interesting properties emerge, said senior author Matthew Yankowitz, assistant professor of physics and of materials science and engineering. But what if you keep adding layers? Eventually, it has to end, right? This is what intuition suggests. But in this case, the intuition is wrong. You can combine 2D properties into 3D materials.

Explore new physics in 3D materials

The research team, which includes scholars from Osaka University and the National Institute for Materials Science in Japan, has adapted a common method for manipulating 2D materials. They stacked 2D sheets together with a small twist angle. The researchers placed a single layer of graphene on top of a thin bulk graphite crystal and introduced a torsion angle of about 1 degree between the two. They found new and unexpected electrical properties not only in the twisted interface, but also within the bulk graphite.

The angle of twist is critical to generating these properties, explained Yankowitz, who is also a faculty member at the UW Clean Energy Institute and the UW Institute for Nano-Engineered Systems. A twisting angle between 2D sheets, like two sheets of graphene, creates what’s called a moiré pattern, which alters the flow of charged particles such as electrons and induces exotic properties in the material.

Unprecedented results and future possibilities

In experiments with graphite and graphene, the twist angle also induced a moiré pattern, yielding some surprising results. A torsion introduced only at the graphene-graphite interface changed the electrical properties of the entire graphite material. When a magnetic field was applied, electrons deep in the graphite crystal exhibited unusual properties similar to those of the twisted interface. Essentially, the single braided graphene-graphite interface has become inextricably mixed with the rest of the bulk graphite.

Although we were generating the moiré pattern only on the graphite surface, the resulting properties spread throughout the entire crystal, said co-lead author Dacen Waters, a UW postdoctoral researcher in physics.

For 2D sheets, moiré patterns generate properties that could be useful for quantum computing and other applications. Inducing similar phenomena in 3D materials unlocks new approaches to studying unusual and exotic states of matter and how to bring them out of the laboratory and into our daily lives.

The entire crystal assumes this 2D state, said co-lead author Ellis Thompson, a UW physics doctoral student. This is a fundamentally new way of influencing the behavior of electrons in a bulk material.

Yankowitz and his team believe their approach to generating a torsion angle between graphene and a bulk graphite crystal could be used to create 2D-3D hybrids of its sibling materials, including tungsten ditelluride and zirconium pentatelluride. This could unlock a new approach to re-engineering conventional bulk material properties using a single 2D interface.

This method could become a really rich playground for studying exciting new physics phenomena in materials with mixed 2D and 3D properties, Yankowitz said.

Reference: Mixed Dimension Moiré Systems of Twisted Graphite Thin Films Jul 19, 2023, Nature.
DOI: 10.1038/s41586-023-06290-3

The co-authors on the paper are UW graduate student Esmeralda Arreguin-Martinez and UW postdoctoral researcher Yafei Ren, both in the Department of Materials Science and Engineering; Ting Cao, an assistant professor of materials science and engineering at UW; Manato Fujimoto of Osaka University; and Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan. The research was funded by the National Science Foundation; the United States Department of Energy; the UW Clean Energy Institute; the Office of the Director of National Intelligence; the Japan Agency for Science and Technology; the Japan Society for the Promotion of Science; the Japanese Ministry of Education, Culture, Sports, Science and Technology; and the MJ Murdock Charitable Trust.

Concession Numbers:

• National Science Foundation: DMR-2041972, MRSEC-1719797, DGE-2140004
• US Department of Energy: DE-SC0019443
• Japan Science and Technology Agency: JPMJCR20T3
• Japan Society for the Promotion of Science: JP21J10775, JP23KJ0339, 19H05790, 20H00354 and 21H05233
• Japan Ministry of Education, Culture, Sports, Science and Technology: JPMXP0112101001