Scientists see spins in 2D magnet — ScienceDaily

All magnets—from the common souvenirs hanging on your refrigerator to the disks that provide your computer’s memory to the powerful versions used in research labs—contain spinning quasiparticles called magnons. The direction of spin of one magnon can affect that of its neighbor, which affects the spin of its neighbor, and so on, giving what are known as spin waves. Information can potentially be transmitted via spin waves more efficiently than electricity, and magnons can serve as “quantum links” that “glue” quantum bits together in powerful computers.

Magnons have enormous potential, but are often difficult to detect without bulky pieces of laboratory equipment. Such setups are suitable for conducting experiments but not for developing devices, said Columbia researcher Xiaoyang Zhu, such as magnonic devices and so-called spintronics. However, seeing magnons can be much easier with the right material: a magnetic semiconductor called chromium sulfide bromide (CrSBr), which can be peeled off into atom-thin, 2D layers, synthesized in the lab of chemistry professor Xavier Roy.

In a new article in NatureZhu and collaborators at Columbia University, Washington University, New York University and Oak Ridge National Laboratory show that magnons in CrSBr can pair with another quasiparticle called an exciton, which emits light, offering researchers a means to “see” a spinning quasiparticle.

While perturbing the magnons with light, they observed oscillations from the excitons in the near-infrared range, which is nearly visible to the naked eye. “For the first time, we can see magnons with a simple optical effect,” Zhu said.

The results can be thought of as quantum transduction, or the conversion of one “quantum” of energy into another, said first author Yun Jun (Eunice) Bae, a postdoctoral fellow in Zhu’s lab. The energy of excitons is four orders of magnitude greater than that of magnons; now, because they pair so strongly, we can easily observe small changes in the magnons, Bae explained. This transduction may one day enable researchers to build quantum information networks that can take information from spin-based quantum bits – which normally have to be spaced millimeters apart – and convert it into light, a form of energy , which can transfer information for hundreds of miles via fiber optics

The coherence time — how long the oscillations can last — was also remarkable, Zhu said, lasting much longer than the experiment’s five-nanosecond limit. The phenomenon can go beyond seven micrometers and persist even when the CrSBr devices are made of just two atom-thin layers, raising the possibility of building nanoscale spintronic devices. These devices could one day be more efficient alternatives to today’s electronics. Unlike electrons in an electric current, which encounter resistance as they move, no particles actually move in a spin wave.

The work was supported by the NSF-funded Columbia Materials and Engineering Research Center (MRSEC), and the material was created at the DOE-funded Energy Frontier Research Center (EFRC). From here, the researchers plan to explore the quantum information potential of CrSBr as well as other candidate materials. “At MRSEC and EFRC, we are investigating the quantum properties of several 2D materials that you can stack like paper to create all kinds of new physical phenomena,” Zhu said.

For example, if magnon-exciton coupling can be detected in other types of magnetic semiconductors with slightly different properties than CrSBr, they can emit light in a wider range of colors. “We are assembling the toolbox to construct new devices with customized properties,” Zhu said.

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Materials provided by Columbia University. Originally written by Ellen Neff. Note: Content may be edited for style and length.

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