Researchers in City College of New York physicist Vinod M. Menon's Laboratory for Nano and Micro Photonics ( LaNMP ) have outlined an emerging frontier in quantum materials: atomically thin systems in which light, magnetism, and electric charge are strongly intertwined. This rapidly evolving field could enable next-generation optoelectronic and quantum technologies leveraging the coupled dynamics of light, charge, and spin.
A review article in Nature Materials titled "Excitons in van der Waals magnetic materials," surveys recent advances by the CCNY team in layered magnetic semiconductors, where light-generated electronic excitations known as excitons interact with magnetic order and spin waves known as magnons. Excitons form when light excites an electron inside a material, leaving behind a positively charged "hole." The electron and hole remain bound together as a neutral but optically active particle. Magnons, by contrast, are collective ripples in a material's magnetic order.
Researchers have long sought to combine exciton-rich semiconductor optics with magnetism, for example by adding magnetic atoms to semiconductors or placing atomically thin semiconductors on magnetic materials. Van der Waals magnetic semiconductors offer a more intrinsic route: the excitons and magnetic moments can arise from the same electronic orbitals inside the crystal, allowing light and magnetism to interact directly.
"In these materials, light and magnetism no longer operate as separate channels," said Pratap Chandra Adak , a postdoctoral researcher in Menon's group and lead author of the Review. "An exciton is not just a passive light-driven excitation sitting on top of the magnetism. It can sense the spin order and magnons, and under the right conditions, even help control the magnetic state itself."
The Review discusses representative material platforms, including chromium triiodide, nickel phosphorus trisulfide, and chromium sulfur bromide. It highlights several phenomena that have emerged across two-dimensional magnets. Excitons can strongly enhance magneto-optical effects, enabling the readout of magnetic states via changes in light polarization. Magnetic order can tune exciton energies and spatial confinement, while exciton–magnon coupling can link optical signals to gigahertz magnetic dynamics. The article also surveys exciton-polaritons — hybrid light–matter particles that can carry optical information through a material.
"Over the past few years, this field has moved from detecting magnetism in atomically thin crystals to actively exploring how magnetic order can control light–matter interactions," said Menon, professor of physics and senior author of the Review. "The goal of this article is to bring those developments into a coherent framework and identify where the field can go next."
The Review also frames possible future directions for technologies that require precise control of light and magnetism at small scales, including magneto-photonic memory and readout, all-optical logic, tunable light-emitting devices, magneto-optic lasers, polaritonic devices, and quantum transducers — devices that convert signals between microwave and optical frequencies for future quantum networks.
Several open challenges remain. Many candidate materials are only partially explored, and researchers need more predictive theoretical tools to describe how excitons, spins, lattice vibrations, and photons interact simultaneously. Promising directions include moiré magnetic excitons, optical control of spin textures, magneto-photonic devices, magnetic exciton-polariton condensation, and microwave-to-optical quantum transduction.
Other co-authors include Florian Dirnberger of the Technical University of Munich; Swagata Acharya of the National Laboratory of the Rockies; Akashdeep Kamra of Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau; and Xiaodong Xu of the University of Washington.
The work at CCNY was supported by DARPA and the Gordon and Betty Moore Foundation.
