Researchers at the City University of New York illustrate the burgeoning field of quantum science centered on materials a few atoms thick. In these systems, light, charge, and magnetism do not operate independently, but are closely linked.
The research is by physicist Vinod M. Menon’s Laboratory for Nano and Micro Photonics (LaNMP). Researchers believe these unusual interactions could eventually support advanced optoelectronic devices and quantum technologies that manipulate light, charge, and electron spin together.
When light and magnetism interact
In a review published in natural materialsTitled “Excitons in Van der Waals Magnetic Materials,” the researchers investigate recent advances in layered magnetic semiconductors. These materials allow light-generated excitations called excitons to interact with magnetic orders and magnetic waves known as magnons.
Excitons are formed when incident light energizes electrons and causes them to move, leaving behind positively charged “holes.” Electrons and holes remain combined, forming electrically neutral particles that can strongly interact with light. Magnon is different. They are collective waves that propagate through the organized magnetic structure of matter.
Scientists have spent years linking the optical properties and magnetism of exciton-rich semiconductors. Previous strategies have included adding magnetic atoms to semiconductors or stacking atomically thin semiconductors on top of magnetic materials.
Van der Waals magnetic semiconductors offer a more direct approach. Within these crystals, excitons and magnetic moments can emerge from the same electronic orbital. This common origin allows light and magnetism to interact within the material itself.
“In these materials, light and magnetism no longer function as separate channels,” said Pratap Chandra Adak, a postdoctoral fellow in Menon’s group and lead author of the review. “Excitons are not just passive light-driven excitations on top of magnetism; they can sense spin orders and magnons, and under the right conditions they can also help control the magnetic state itself.”
Read magnetic state with light
This review investigates several important material platforms, including chromium triiodide, nickel phosphorus trisulfide, and sulfur chromium bromide. Studies of these two-dimensional magnets have revealed several ways in which exciton and magnetic behavior can interact.
Excitons can greatly enhance magneto-optic effects, allowing scientists to identify magnetic states by observing changes in the polarization of light. Magnetic order changes the energy of excitons and can also affect where excitons are confined within the material.
Interactions between excitons and magnons allow coupling optical signals with magnetic activity occurring at gigahertz frequencies. Researchers are also discussing exciton-polaritons, hybrid particles that combine the properties of light and matter and can transmit optical information through matter.
“Over the past few years, the field has moved from detecting magnetism in atomically thin crystals to actively exploring how magnetic ordering can control the interaction of light and matter,” said Menon, professor of physics and lead author of the review. “The purpose of this article is to bring these developments together into a coherent framework and identify where the field should go next.”
New possibilities of quantum technology
Researchers have identified several applications that may rely on precise control of light and magnetism at very small scales. These include magneto-photonic memory and data readout, all-optical logic, tunable light-emitting devices, magneto-optic lasers, and polaritonic technologies.
Another promising application involves quantum transducers. These devices convert signals between microwave and optical frequencies. This feature could be important for connecting components in future quantum networks.
Significant scientific challenges remain
Despite rapid progress, much of this field remains unexplored. Many possible materials have not yet been studied in detail, and scientists still need better theoretical models that can predict how excitons, electron spins, lattice vibrations, and photons will behave when they interact together.
Future research could explore moire magnetic excitons, optical control of spin textures, magnetophotonic devices, magnetic exciton-polariton condensation, and conversion of microwave signals to optical signals for quantum communications.
Other co-authors include Florian Dirnberger from the Technical University of Munich. Swagata Acharya of the National Laboratory of the Rockies. Akashdeep Kamra from Rhineland-Palatinate University of Technology in Kaiserslautern-Landau. and Xiaodong Xu of the University of Washington.
Research at CCNY was supported by DARPA and the Gordon and Betty Moore Foundation.
