Scientists see spins in a 2D magnet

All magnets – from simple memories hanging on your fridge to disks that give your computer memory to powerful versions used in research labs – contain spinning quasi-particles called magnons. The direction in which a magnon spins can influence that of its neighbour, which affects its neighbour’s spin, and so on, producing what are called spin waves. Information can potentially be transmitted via spin waves more efficiently than with electricity, and magnons can serve as “quantum interconnects” that “glue” quantum bits together in powerful computers.

Magnons have enormous potential, but they are often difficult to detect without bulky laboratory equipment. Such setups are great for conducting experiments, but not for developing devices, said Columbia researcher Xiaoyang Zhu, such as magnonic devices and so-called spintronics. Seeing magnons can be made much simpler, however, with the right material: a magnetic semiconductor called chromium sulfide bromide (CrSBr) that can be peeled into atom-thin 2D layers, synthesized in Professor Xavier’s lab Roy from the chemistry department.

In a new article from NatureZhu and collaborators from Columbia, University of Washington, New York University, and Oak Ridge National Laboratory show that CrSBr magnons can associate with another quasiparticle called an exciton, which emits of light, giving researchers a way to “see” the spinning quasiparticle.

By perturbing the magnons with light, they observed oscillations of the excitons in the near-infrared region, which is almost 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 “quanta” of energy into another, said first author Youn Jun (Eunice) Bae, a postdoc in Zhu’s lab. The energy of excitons is four orders of magnitude greater than that of magnons; now, because they pair so tightly, we can easily observe tiny changes in the magnons, Bae explained. This transduction could one day allow researchers to build quantum information networks that can take information from spin-based quantum bits – which typically need to be located within millimeters of each other – and convert them into light. , a form of energy capable of transferring information upwards. hundreds of kilometers away via fiber optics

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 could travel more than seven micrometers and persist even when the CrSBr devices were made of only two thin layers of atoms, 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 particle actually moves in a spin wave.

From there, the researchers plan to explore the quantum information potential of CrSBr, as well as other candidate materials. “In MRSEC and EFRC, we explore the quantum properties of multiple 2D materials that you can stack like papers to create all kinds of new physical phenomena,” Zhu said.

For example, if the magnon-exciton coupling can be found in other types of magnetic semiconductors with slightly different properties from CrSBr, they could emit light in a wider color range.

“We are assembling the toolkit to build new devices with customizable properties,” Zhu added.