Nanotechnology

With the new experimental method, the researchers investigated the structure of spins in 2D materials for the first time

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May 11, 2023

(Nanowerk News) For two decades, physicists have been trying to directly manipulate the spin of electrons in 2D materials such as graphene. Doing so could trigger important advances in the emerging world of 2D electronics, a field where superfast, small, and flexible electronic devices perform calculations based on quantum mechanics.

The caveat is that the typical way in which scientists measure electron spin – the essential behavior that gives everything in the physical universe its structure – usually doesn’t work in 2D matter. This makes it very difficult to fully understand the materials and drive technological advances based on them. But a team of scientists led by Brown University researchers believe they now have a way out of this longstanding challenge. They describe their solution in a new study published in Natural Physics (“Dirac awakening drives a resonance response in twisted two-layer graphene”). direct interaction between rotating electrons in 2D materials and photons coming from microwave radiation In the study, the researchers describe what they believe are the first measurements demonstrating a direct interaction between electrons spinning in a 2D material and photons originating in microwave radiation. (Image: Jia Li, Brown University)

In the study, the team – which also includes scientists from the Center for Integrated Nanotechnology at Sandia National Laboratory, and the University of Innsbruck – describe what they believe to be the first measurements demonstrating a direct interaction between electrons spinning in 2D matter and incident photons. from microwave radiation. Called coupling, the absorption of microwave photons by electrons establishes a new experimental technique for directly studying the properties of how electrons spin in these 2D quantum materials — which could serve as a basis for developing computing and communications technologies based on them, according to the researchers.

“Spin structure is an important part of quantum phenomena, but we’ve never really investigated it directly in these 2D materials,” said Jia Li, assistant professor of physics at Brown and senior author of the research. “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 study many different systems that we couldn’t before.”

The researchers performed the measurements on a relatively new 2D material called “magic-angle” bent double-layer graphene. This graphene-based material is created when two sheets of ultrathin layers of carbon are stacked and rotated to a precise angle, turning the new two-layer structure into a superconductor that allows electricity to flow without resistance or wastage of energy. Newly discovered in 2018, researchers are focused on the material because of its potential and the mystery that surrounds it.

“A lot of the big questions asked in 2018 are still unanswered,” said Erin Morissette, a graduate student in Li’s lab at Brown who led the research.

Physicists usually use nuclear magnetic resonance or NMR to measure the spin of electrons. They did this by examining the nuclear magnetic properties in the sample material using microwave radiation and then reading the different signatures that this radiation produced to measure spin.

The challenge with 2D materials is that the magnetic signature of electrons in response to microwave excitation is too small to detect. The research team decided to improvise. Instead of directly detecting the magnetization of the electrons, they measured subtle changes in electronic resistance, caused by changes in the magnetization of the radiation using a device built at the Institute for Molecular and Nanoscale Innovation at Brown. Tiny variations in the flow of electronic currents allowed researchers to use the device to detect that electrons absorb the photo of microwave radiation.

Researchers can observe new information from experiments. The team noticed, for example, that the interactions between photons and electrons made electrons in certain parts of the system behave as they would in an anti-ferromagnetic system—meaning the attractions of some atoms were canceled out by a set of magnetic atoms aligned in the opposite direction.

The new method for studying spins in 2D materials and the current findings would not apply to current technology, but the research team sees the potential applications this method could generate in the future. They plan to continue applying their method to bent two-layer graphene, but also extend it to other 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,” says Morissette.

The experiment was conducted remotely in 2021 at the Center for Integrated Nanotechnologies in New Mexico. Mathias S. Scheurer from the University of Innsbruck provided theoretical support for the modeling and understanding of the results.



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