Researchers Surf the Magnon Wave To Control Particles in Next-Gen Electronics
Study Reveals the Potential of Magnon ‘Currents’ for Cutting-Edge Technologies
A new study demonstrates how magnons, a type of wave found in magnetic systems, can manipulate interactions between excitons—uncharged “quasiparticles” that carry energy. This discovery provides insights for tuning exciton behavior in quantum technologies, opening the door to cutting-edge applications.
Two researchers from NREL, alongside researchers from colleges and universities in New York, Florida, the Czech Republic, Germany, England, and Spain, demonstrated that in a certain class of magnetic semiconductor materials, electron pair interactions, which form the backbone of many next-generation electronic devices, can be controlled by linking magnetic and charge excitations. They deployed a theoretical quantum-mechanical framework they created to explain these observations. This new finding, guided by the theory, could lead to the development of quantum transducers—devices that are crucial for quantum communication and computing technologies.
“The observation that magnetic fields can modulate the particle-particle interactions in these materials is transformative to our understanding of magnetic semiconductors,” said Mark van Schilfgaarde, NREL’s chief theorist who contributed to this study. “Understanding such highly complex phenomena has only recently become feasible due to major advances in theory methods and in computing power. Our study benefited greatly from these advances and from the direct collaboration with experimental groups.”
The research team published their findings in a paper published in Nature Materials, titled “Magnon-Mediated Exciton–Exciton Interaction in a van der WaalsAntiferromagnet”. Funding for this work was provided by the U.S. Department of Energy’s Office of Science Basic Energy Sciences, with additional support from the National Science Foundation, Army Research Office, Office of Naval Research, Gordon and Betty Moore Foundation, Simons Foundation, Spanish Ministry of Science, Innovation, and Universities, and Czech Ministry of Education, Youth, and Sports.
Understanding the Formation of Excitons and Magnons
Even though they are invisible to the naked eye, excitons are a “quasiparticle” commonly found within everyday electronic devices—from solar panels to LED lights, and even smartphones.
When light hits a substance, it can energize an electron, causing it to jump to a higher energy level and leave behind a “hole” or missing electron. This electron and hole, which are attracted to each other due to their opposite charges, can either separate quickly and act independently, or stay close together and form a combined entity known as an exciton. This exciton is an excited state that behaves like a single, neutral “quasiparticle.” The process can also be reversed, with the electron releasing light and returning to its original state, thereby annihilating the exciton. This phenomenon is the basis for many advanced electronic devices, as it affects how these materials absorb and emit light. Different excitons within a material can carry energy over varying distances and have different energy levels, offering numerous possibilities for new types of optoelectronics.
“The excitons within a material vary greatly in their binding energy, which affects their ability to carry energy over small or large distances,” said NREL’s Swagata Acharya, who carried out the primary theoretical research in this study. “The ability to control them provides a rich playground for developing many new kinds of electronics by influencing how they absorb and emit light.”
In the same way that excitons affect a material’s optical properties, magnons provide a pathway to manipulate a material’s magnetic properties. Each electron—whether part of an exciton or not—contains an invisible compass needle (axis) oriented in one of two directions, known as its “spin.” Electrons within the same material do not always align the same way, and the resulting pattern of electron spins affects how they respond to magnetic fields. External influences, such as temperature changes or energy absorption, can cause the electron spins to shift and tremble, producing waves called magnons. Much like light, magnons exhibit both wave-like properties (such as frequency and wavelength) and particle-like behavior (such as energy and momentum transfer).
Discovering a Pathway To Control Exciton Interactions
The research team selected chromium sulfide bromide (CrSBr) for their study. CrSBr is a layered material like graphite—bonds within a sheet are strong, while sheets bind to each other very weakly. This makes CrSBr quasi-two dimensional. Owing to its layered nature, it is a magnetic semiconductor that supports both excitons and magnons while efficiently absorbing and emitting light.
The team used experimental techniques like applying different magnetic fields and illuminating the material with varying intensities of light to cause excitons to form.
They made an important new observation based on these experiments. Typically, when light gives energy to electrons in a material, it leads to the formation of excitons, and as more light is absorbed, the density of excitons increases. As the excitons are driven closer together, they repel each other, which raises their energy. However, in this study, the researchers applied an external magnetic field, disturbing the electron spins and generating magnons. As magnons formed, the excitons attracted each other instead, lowering their energy at a much faster rate than would normally occur. The result? A “nonlinear redshift” in exciton energy—that is coupled to the magnetism.
“What’s happening here is that at a finite magnetic field where the spins are canted, as the exciton density increases, that in turn affects the angle between the sublattice spins,” said City College of New York’s Vinod Menon, professor who was the originator of this study. “This in turn also affects the overall exciton energy; it reduces still more due to more interlayer coupling.”
The theoretical modeling performed by the NREL researchers elucidated the precise role that magnons play to drive the nonlinear optical effects observed experimentally and pointed the way towards advanced, magnetically tunable technologies based on this class of materials.
Implications of Controlling Exciton Interactions With Magnons
Beyond CrSBr, the team’s discovery of harnessing magnon-mediated exciton interactions opens the door to a range of applications. Optical devices that respond to low-intensity light could be refined with this mechanism, yielding cameras that more accurately detect subtle changes in light. Quantum transducers that bridge microwave and optical signals could be improved to yield faster and more reliable internet speeds and communication networks. Next-generation processors that use light instead of electricity to process information could yield faster, more efficient processors for devices such as computers and phones.
“Low-dimensional magnetic materials, and CrSBr in particular,” said Acharya, “offer a very promising medium for next-generation applications in photonics, quantum computing, sensing, and transduction. Owing to our advanced theoretical framework we can now understand the extraordinarily complex interactions between light and magnetism occurring in these materials.”
Learn more about basic energy sciences at NREL and about the U.S. Department of Energy's Office of Science Basic Energy Sciences program. Read "Magnon-Mediated Exciton–Exciton Interaction in a van der Waals Antiferromagnet" in Nature Materials.
Last Updated May 28, 2025