Researchers Achieve Breakthrough in 2D Electronics by Observing Spin Structure in “Magic-Angle” Graphene

A team of researchers, led by scientists from Brown University, has overcome a significant obstacle in the field of two-dimensional (2D) electronics. They achieved this breakthrough by investigating the spin structure in “magic-angle” graphene.

For the past two decades, physicists have been striving to manipulate the spin of electrons in 2D materials, such as graphene. The ability to control electron spin could revolutionize the field of 2D electronics, enabling the development of ultra-fast, compact, and flexible electronic devices based on quantum mechanics.

However, a major challenge has been the difficulty in directly measuring electron spin, a fundamental property that determines the structure of everything in the physical universe, in 2D materials. This limitation has hindered our understanding of these materials and impeded technological advancements based on them. Nevertheless, a team of scientists, including researchers from Brown University, has devised a solution to this longstanding challenge. Their findings are presented in a recent study published in Nature Physics.

In their study, the team, which also involved scientists from the Center for Integrated Nanotechnologies at Sandia National Laboratories and the University of Innsbruck, describe the first measurement showing direct interaction between electrons’ spin in a 2D material and photons emitted by microwave radiation. This coupling of microwave photons with spinning electrons offers a novel experimental technique for studying the spin properties of 2D quantum materials. The researchers believe that this breakthrough could lay the foundation for advancements in computational and communication technologies based on these materials.

Jia Li, an assistant professor of physics at Brown and the senior author of the research, explained, “Spin structure is the most important part of a quantum phenomenon, but we’ve never really had a direct probe for it in these 2D materials. That challenge has prevented us from theoretically studying spin in these fascinating materials for the last two decades. We can now use this method to study a lot of different systems that we could not study before.”

The team conducted their measurements on a relatively new 2D material called “magic-angle” twisted bilayer graphene. By stacking and twisting two ultrathin carbon sheets to a precise angle, this graphene-based material transforms into a superconductor that allows the flow of electricity without resistance or energy loss. Discovered in 2018, the material holds great promise and intrigue, as many questions surrounding its properties remain unanswered.

Traditionally, physicists utilize nuclear magnetic resonance (NMR) to measure electron spin. This involves exciting the nuclear magnetic properties in a sample material using microwave radiation and analyzing the resulting signatures to determine spin. However, 2D materials present a challenge because the magnetic signatures of electrons in response to microwave excitation are too faint to detect. To overcome this hurdle, the research team devised an alternative approach. Instead of directly measuring electron magnetization, which was challenging in 2D materials, they measured subtle changes in electronic resistance caused by the radiation-induced magnetization changes. The team fabricated a device at the Institute for Molecular and Nanoscale Innovation at Brown to detect these small variations in electronic currents, revealing that electrons were absorbing photons from the microwave radiation.

During the experiments, the researchers made exciting observations. For example, they noted that the interaction between photons and electrons caused specific sections of the system to behave like an anti-ferromagnetic system, where the magnetism of certain atoms was canceled out by a set of aligned magnetic atoms in the opposite direction.

Although the new method and findings are not immediately applicable to current technology, the research team foresees potential future applications. They plan to continue applying their method to twisted bilayer graphene and extend it to other 2D materials. Erin Morissette, a graduate student in Li’s lab at Brown who led the research, expressed, “It’s a really diverse toolset that we can use to access an important part of the electronic order in these strongly correlated systems and, in general, to understand how electrons can behave in 2D materials.”

The experiment was conducted remotely in 2021 at the Center for Integrated Nanotechnologies in New Mexico. Theoretical support for modeling and understanding the results was provided by Mathias S. Scheurer from the University of Innsbruck. Funding for the research came from the National Science Foundation, the U.S. Department of Defense, and the U.S. Department of Energy’s Office of Science.

Frequently Asked Questions (FAQs) about 2D electronics

More about 2D electronics

• Nature Physics
• Brown University
• Center for Integrated Nanotechnologies
• University of Innsbruck
• National Science Foundation
• U.S. Department of Defense
• U.S. Department of Energy’s Office of Science