A group of researchers from Brown University were able to find a solution for a long-standing problem in the world of two-dimensional electronics by closely studying the spin structure in “magic-angle” graphene.
For many years, physicists have been trying to learn how to control the spin of electrons in 2D materials like graphene. This would allow us to make advances in 2D electronics, but there has been a problem: the usual measurements for electron spin haven’t worked with these materials. A team of researchers from Brown University figured out the solution and published their work in Nature Physics. They became the first people ever to connect electrons spinning around in a 2D material directly with microwave radiation photons. With this invention, it will be possible to explore the properties of electron spin when it comes to quantum materials, which might lead us to making new technology based upon them – like computers or ways of communicating.
For twenty years, scientists have been trying to control the direction of electrons in thin materials like graphene. If successful, this could help us make tiny electronic devices that run quickly and are bendy– these use laws from quantum science when carrying out their work.
It’s usually tough for scientists to measure the spinning of electrons, which is really important for giving everything in our universe a shape. But recently a group of researchers led by Brown University researchers probably found a way to do it. They wrote about their plan on May 11th in Nature Physics magazine.
In the study, researchers from some organizations like Sandia National Laboratories and the University of Innsbruck showed us an interesting new way. They discovered that it is possible for electrons spinning in 2D materials to actually interact directly with photons that come from microwave radiation. This interaction between the electrons and photons is called a coupling. It helps us understand how electrons move around in these 2D quantum materials, which might help us develop better technologies to do things like computing or communication!
Scientists have been having a hard time studying spins in two dimensional materials for the past twenty years because they didn’t know how to directly investigate it. Jia Li, a physics professor at Brown University, figured out a way to probe this spin structure and understand this quantum phenomenon better. Now we can use this new method to explore things we couldn’t before!
Researchers studied a special material made from two sheets of very thin carbon layers that have been stacked and twisted into an angle called “magic-angle”. This double-layered structure, discovered in 2018, is what makes it possible for electricity to flow with no resistance or energy loss – so it’s known as a superconductor. People are interested in this because it has lots of amazing potential.
Erin Morissette, a graduate student from Brown University’s Li lab said that many important questions asked in 2018 have yet to be answered. Scientists usually use something called NMR (nuclear magnetic resonance) to measure the spinning of electrons. To do this, they send out a special type of energy wave called microwave radiation which affects the nuclear magnetic properties of a material and then read the different signals generated by this radiation to figure out how fast the electron is spinning.
The scientists had a problem; they couldn’t detect the magnetic signals from electrons that were stimulated by microwave radiation. To fix this, they made a device at Brown University’s Institute for Molecular and Nanoscale Innovation. This device measured slight changes in electric resistance due to magnetization from the radiation. They used this devise to see that the electrons were absorbing energy from the microwaves.
The scientists did experiments and saw something unusual. For example, when the photons and electrons interacted with each other, some of the atoms changed in a way that made them act like magnets that have opposite poles – meaning one group had their magnets pointing in one direction while another group had theirs pointing the opposite way.
Researchers have come up with a new way to study 2D materials using spin. This won’t help us with modern technology, but the researchers think it could be useful in the future. They plan to use this method on twisted bilayer graphene and other 2D materials too.
We have a lot of tools to use so that we can learn more about electronic orders in materials that are closely related. We will be able to better understand the way electrons move around in 2D materials. Said Morissette.
Researchers from around the world have collaborated together in a project and published a paper in Nature Physics called “Dirac Revivals Drive a Resonance Response in Twisted Bilayer Graphene”. In this paper, they present their findings that can explain some of the mysterious behaviour of twisted bilayer graphene. This paper was published on the 11th of May 2023, and you can find it by looking for its DOI number: 10.1038/s41567-023-02060-0.
In 2021, a very special experiment was conducted at the Center for Integrated Nanotechnologies in New Mexico. Mathias S. Scheurer from University of Innsbruck helped to model and understand its outcome. To make this experiment happen, money was donated by some important organizations such as the National Science Foundation, the U.S. Department of Defense and the U.S. Department of Energy’s Office of Science.
