According to research, spinning quasiparticles, known as magnons, light up when paired with a light-emitting quasiparticle, known as an exciton, which has potential quantum information applications.
Magnets contain spinning quasiparticles called magnons, which can range from simple souvenirs on your refrigerator to the discs that store your computer’s memory to the powerful versions used in research labs. The spin of one magnon can affect the spin of its neighbor, which affects the spin of its neighbor, and so on, producing what are known as spin waves. Spin waves have the potential to transmit information more efficiently than electricity, and magnons can act as “quantum interconnects,” “gluing” quantum bits together to form powerful computers.
Magnons have enormous potential, but they are often difficult to detect without the use of bulky laboratory equipment. Such setups are fine for conducting experiments, but not for developing devices, such as magnonic devices and so-called spintronics, according to Columbia researcher Xiaoyang Zhu. Seeing magnons can be made much simpler with the right material: a magnetic semiconductor called chromium sulfide bromide (CrSBr) that can be peeled into atom-thin, 2D layers and was synthesized in the lab of Department of Chemistry professor Xavier Roy.
If magnon-exciton coupling is found in other types of magnetic semiconductors with slightly different properties than CrSBr, for example, they may emit light in a wider range of colors. We’re putting together the toolbox to build new devices with customizable properties.
Xiaoyang Zhu
In a new article in Nature, Zhu and collaborators at Columbia, the University of Washington, New York University, and Oak Ridge National Laboratory show that magnons in CrSBr can pair up with another quasiparticle called an exciton, which emits light, offering the researchers a means to “see” the spinning quasiparticle.
As they perturbed 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 findings could be interpreted as quantum transduction, or the conversion of one “quanta” of energy to another, according to first author Youn Jun (Eunice) Bae, a postdoc in Zhu’s lab. Excitons have four orders of magnitude more energy than magnons; now, because they pair so strongly, we can easily observe tiny changes in the magnons, according to Bae. This transduction may one day allow researchers to build quantum information networks that can convert information from spin-based quantum bits (which generally need to be within millimeters of each other) to light, a form of energy that can transfer information hundreds of miles via optical fibers.
The coherence time, or how long the oscillations can last, was also remarkable, according to Zhu, lasting much longer than the experiment’s five-nanosecond limit. The phenomenon could travel over seven micrometers and persist even when the CrSBr devices were made of only two atom-thin layers, implying that nano-scale spintronic devices could be built. These devices may one day be more efficient than today’s electronics. In a spin wave, unlike electrons in an electrical current, which encounter resistance as they travel, no particles are actually moving.
The work was funded by the NSF-funded Materials Research Science and Engineering Center (MRSEC) at Columbia, and the material was developed at the DOE-funded Energy Frontier Research Center (EFRC). From here, the researchers intend to investigate the quantum information potential of CrSBr as well as other material candidates. “At the MRSEC and EFRC, we are investigating the quantum properties of several 2D materials that can be stacked like papers to produce a variety of new physical phenomena,” Zhu explained.
If magnon-exciton coupling is found in other types of magnetic semiconductors with slightly different properties than CrSBr, for example, they may emit light in a wider range of colors. “We’re putting together the toolbox to build new devices with customizable properties,” Zhu explained.
