Magnon Spins Observed in 2D Magnets

According to the latest issue of “Nature” magazine, the collaborative research of several universities in the United States and Oak Ridge National Laboratory shows that the magnons in the magnetic semiconductor chromium bromide can pair with excitons, and the excitons will emit light, thus providing a new way for research. Researchers offer a way to “see” spinning quasiparticles.

The pairing between magnons and excitons will allow researchers to see spin orientation, an important consideration for quantum applications.

All magnets, from simple refrigerator magnets to memory disks in computers to powerful magnets used in laboratory research, contain spinning quasiparticles called magnons. The direction in which a magnon spins can affect the direction of its “neighbor,” which in turn affects the spin of that “neighbor,” and so on, producing spin waves. Information can be transmitted by spin waves more efficiently than electricity, and magnons can act as “quantum interconnects” that “glue” qubits into powerful computers.

Magnon Spins Observed in 2D Magnets

Magnon Spins Observed in 2D Magnets

Magnons are often difficult to detect without bulky laboratory equipment. Observing magnons, however, can be made simpler with the right material: a magnetic semiconductor called chromium bromide, which can be exfoliated into atomically thin two-dimensional layers.

When the magnons were perturbed with light, the researchers observed oscillations of the excitons in the near-infrared range, which is nearly visible to the naked eye. This is the first time researchers have seen magnons with simple optical effects.

The researchers say the result can be thought of as quantum transduction, or the conversion of one “quantum” of energy into another. Excitons are four orders of magnitude more energetic than magnons, and because they are so tightly paired together, researchers can easily observe tiny changes in magnons. This kind of transduction can help build quantum information networks that need to take information from spin-based qubits located a few millimeters away from each other and convert it into light, a method that can transmit information to digital objects through optical fibers. The form of energy that is hundreds of kilometers away.

The coherence time (how long the oscillations can last) is also significant, much longer than the experiment’s 5-nanosecond limit, the study showed. This phenomenon can propagate beyond 7 micrometers and persist even when chromium bromide devices are made of just two atomically thin layers, raising the possibility of building nanoscale spintronic devices. These devices promise to be more effective replacements for today’s electronics in the future. Unlike electrons in an electric current, which encounter resistance as they travel, no particles actually move in a spin wave.

Starting from the quantum information potential of chromium bromide, the researchers plan to explore the quantum properties of other 2D materials. By stacking these materials like paper, various new physical phenomena are created. For example, if magnetoexciton coupling could be found in other magnetic semiconductors with slightly different properties than chromium bromide, they might emit light in a wider range of colors.

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