A group of researchers led by Chocolate University researchers found a solution to an old roadblock in two-dimensional electronics by analyzing the structure of the spins in “magic-angle” graphene.
Over the last two decades, physicists have been trying to change the spin of electrons in 2D materials such as graphene. This could lead to significant breakthroughs in the field of developing 2D electronics, which use superfast, tiny, and flexible electronic devices to perform quantum mechanical computations.
Conventional methods for measuring the spin of electrons—a critical feature that gives structure to everything in the physical universe—often don’t work in 2D matter. This makes it very difficult to fully understand the material and make technical progress based on it.
However, a group of scientists led by Brown University researchers believe they have found a solution to this longstanding problem. In new research published in Natural Physicsthey detail their solutions.
The group, which also includes scientists from Sandia National Laboratories and the University of Innsbruck, describes what they believe is the first measurement of the direct interaction between electrons spinning in a 2D material and photons emitted by microwave radiation on paper.
The absorption of microwave photons by electrons, known as coupling, forms an innovative experimental technique for effectively studying the properties of how electrons spin in these 2D quantum materials — which, the investigators say, could form the basis for developing computing and communications. technology based on these materials.
Spin structures are an important part of quantum phenomena, but we’ve never really investigated them directly in these 2D materials. That challenge has prevented us from studying spin theoretically in this exciting material for the past two decades. We can now use this method to learn many different systems that we couldn’t learn before.
Jia Li, Senior Author of the Study and Assistant Professor, Brown University
The observations were made on a relatively new 2D material known as “magic-angle” bent double-layer graphene. This graphene-based material is formed by stacking two sheets of ultrathin carbon layers and twisting them at precise angles, creating a superconductor that allows electricity to flow without resistance or wastage of energy. Unearthed in 2018, investigators have concentrated on the material for its potency and mystery.
“Many of the big questions asked in 2018 are still unansweredsaid Erin Morissette, a graduate student in the Li lab at Brown who guided the work.
Nuclear magnetic resonance, or NMR, is commonly used by physicists to determine the spin of electrons. They did this by using microwave radiation to generate the nuclear magnetic characteristics of the sample material and then reading the different signals caused by the radiation to calculate the spin.
The problem with 2D materials is that the magnetic signature of electrons due to microwave excitation is too small to detect. The study team decided to improvise.
Instead of directly feeling the magnetization of the electrons, they assessed tiny variations in electronic resistance caused by changes in magnetization produced by radiation using a device built at Brown’s Institute for Molecular and Nanoscale Innovation. Due to slight fluctuations in the flow of electronic currents, the researchers were able to utilize the device to identify that the photo-absorbing electrons of the microwave radiation.
Experiments provide researchers with new information. For example, the team found that the interaction between photons and electrons causes electrons in certain parts of the system to start behaving like in an anti-ferromagnetic system — that is, the attraction of some atoms is canceled out by a magnetized set of atoms. aligned in the opposite direction.
The new technique for investigating spins in 2D materials and its current discovery is useless for current technology, but the research team envisions future applications of this method. They intend to continue using this technology on bent two-layer graphene while also extending it to additional 2D materials.
“These are very diverse tools that we can use to access important parts of the electronic order in these highly correlated systems and generally to understand how electrons might behave in 2D materials.said Morissette.
This study was funded by the National Science Foundation, the US Department of Defense, and the US Department of Energy’s Office of Science.
Morissette, E., et al. (2023). The awakening of Dirac drives a resonance response in bent bilayer graphene. Natural Physics. doi.org/10.1038/s41567-023-02060-0.