The pursuit of next-generation computing and communication technologies has led researchers to the very edge of material science, where the traditional boundaries between light, electricity, and magnetism begin to dissolve. At the City College of New York (CCNY), a team of physicists led by Vinod M. Menon is currently mapping this frontier, focusing on a specialized class of materials known as van der Waals (vdW) magnetic semiconductors. These substances, which can be thinned down to a layer only a few atoms thick, represent a paradigm shift in quantum science. Unlike conventional materials where optical and magnetic properties operate in isolation, these 2D systems exhibit a profound interconnectedness, allowing for the simultaneous manipulation of photons, charges, and electron spins.
The findings, detailed in a comprehensive review titled "Excitons in van der Waals magnetic materials" and published in the journal Nature Materials, synthesize years of progress within the Laboratory for Nano and Micro Photonics (LaNMP). The research suggests that the unique interactions found in these layered magnets could provide the bedrock for advanced optoelectronic devices and quantum technologies that surpass the limitations of current silicon-based architecture.
The Evolution of Two-Dimensional Material Science
To understand the significance of the work at CCNY, one must look at the trajectory of material science over the last two decades. The field of 2D materials was effectively inaugurated in 2004 with the isolation of graphene—a single layer of carbon atoms. While graphene revolutionized the understanding of electrical conductivity at the atomic scale, it lacked intrinsic magnetic properties and a bandgap, which limited its utility in complex optical and switching applications.
For years, the scientific community sought "the graphene of magnetism"—a material that could maintain stable magnetic order at the monolayer limit. This search reached a turning point in 2017 when researchers identified magnetic order in 2D crystals such as chromium triiodide (CrI3) and iron germanium telluride (Fe3GeTe2). Since then, the field has expanded rapidly. The recent review by Menon’s team marks a transition from the mere discovery of these materials to the active engineering of their quantum states.
Historically, integrating magnetism with semiconductors required complex "doping" processes—injecting magnetic impurities into a non-magnetic host—or creating "heterostructures" by stacking different materials on top of one another. While effective, these methods often resulted in weak interactions or structural defects. Van der Waals magnetic semiconductors offer a more elegant solution: the magnetism and the optical properties are inherent to the same crystal lattice, emerging from the same electronic orbitals. This internal synergy allows for a level of control that was previously thought unattainable.
Understanding the Quasiparticle Interaction: Excitons and Magnons
At the heart of this research are two distinct yet interacting phenomena: excitons and magnons.
An exciton is a quasiparticle that forms when a photon strikes a semiconductor. The energy from the light kicks an electron into a higher energy state, leaving behind a "hole"—a void that acts as a positive charge. Due to electrostatic attraction, the electron and the hole remain bound together, orbiting one another as they move through the material. Because excitons are electrically neutral but highly sensitive to light, they are the primary vehicles for carrying information in optoelectronic devices.
Magnons, on the other hand, are collective excitations of the material’s magnetic moments, or "spins." Rather than a single particle moving, a magnon is a wave of spin-alignment changes that ripples through the magnetic structure of the crystal. In traditional materials, excitons and magnons rarely "speak" to one another. However, in vdW magnetic semiconductors, the two are inextricably linked.
"In these materials, light and magnetism no longer operate as separate channels," explained Pratap Chandra Adak, a postdoctoral researcher at CCNY and the 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."
This coupling means that by hitting a material with a pulse of light, scientists can potentially flip its magnetic orientation or generate a burst of magnetic waves. Conversely, by changing the magnetic environment, they can alter how the material absorbs or emits light.
Material Platforms and Experimental Data
The CCNY review highlights three specific material platforms that have become the workhorses of this new field: chromium triiodide (CrI3), nickel phosphorus trisulfide (NiPS3), and chromium sulfur bromide (CrSBr).
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Chromium Triiodide (CrI3): This was the first material to demonstrate that magnetism could persist in a single atomic layer. Data from various studies show that CrI3 exhibits a strong magneto-optical Kerr effect (MOKE), where the polarization of reflected light changes based on the magnetic state of the material. This makes it an ideal candidate for optical memory readout.
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Nickel Phosphorus Trisulfide (NiPS3): Unlike CrI3, which is a ferromagnet (where spins point in the same direction), NiPS3 is an antiferromagnet (where spins point in alternating directions). Recent experiments have shown that NiPS3 hosts "coherent excitons" that are extremely sensitive to the underlying magnetic lattice, allowing researchers to track complex magnetic phase transitions using only light.
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Chromium Sulfur Bromide (CrSBr): This material is particularly promising because of its high "Néel temperature"—the temperature at which it becomes magnetic. While many 2D magnets only function at temperatures near absolute zero, CrSBr remains magnetic at much higher thresholds, bringing the technology closer to real-world room-temperature applications. It also exhibits strong coupling between excitons and magnons at gigahertz frequencies, which is the standard frequency range for modern telecommunications.
Implications for Quantum Computing and Data Storage
The ability to link optical signals with magnetic states has profound implications for the future of information technology. One of the most anticipated applications is the development of "quantum transducers."
In the current quantum landscape, different systems are good at different things. Superconducting qubits, like those used by IBM and Google, operate at microwave frequencies but are difficult to transmit over long distances. Photons (light), however, are excellent for carrying information over fiber-optic cables. A vdW magnetic semiconductor could act as a bridge, converting a magnetic/microwave signal from a processor into an optical signal for transmission, and then back again at the destination.
Furthermore, the research points toward the creation of magneto-photonic memory. Modern hard drives use magnetic fields to write data and electronic sensors to read it. A system based on vdW magnets could use light to both read and write data, potentially increasing speeds by orders of magnitude while drastically reducing power consumption.
The review also discusses "exciton polaritons"—hybrid particles that are part-light and part-matter. In vdW magnets, these polaritons can be used to create "topological insulators" for light, where information can flow around defects without being scattered or lost. This could lead to the development of all-optical logic gates, which would perform computations using light instead of electricity, bypassing the heat issues that plague modern microchips.
Strategic Importance and Global Research Context
The work at CCNY does not exist in a vacuum. It is part of a global race to dominate the quantum technology sector. The Review co-authors include experts from the Technical University of Munich, the National Laboratory of the Rockies, the University of Washington, and the University of Kaiserslautern-Landau, highlighting the international and collaborative nature of this research.
The funding for this work reflects its strategic value. Supported by the Defense Advanced Research Projects Agency (DARPA) and the Gordon and Betty Moore Foundation, the research aligns with broader national interests in securing a lead in quantum information science (QIS). DARPA’s involvement, in particular, suggests that the long-term applications of these materials—such as ultra-secure communication and high-speed signal processing—are viewed as critical for future defense and infrastructure.
Scientific Challenges and the Road Ahead
Despite the optimism, the transition from laboratory review to industrial application faces significant hurdles. The CCNY team identifies several "grand challenges" that the scientific community must address in the coming decade.
First, there is the "temperature problem." While CrSBr shows promise, most 2D magnetic materials still require cryogenic cooling to maintain their properties. For these materials to be integrated into consumer electronics, researchers must find or engineer vdW magnets that are stable at room temperature.
Second, there is a need for more robust theoretical frameworks. The interaction between excitons, magnons, and the crystal lattice (phonons) is incredibly complex. Current models often struggle to predict how these four components—light, charge, spin, and vibration—will behave when they are all interacting simultaneously in a non-linear fashion.
Finally, the field is looking toward "moiré" engineering. By stacking two layers of 2D materials and twisting them at a specific angle, researchers can create a moiré pattern—a superlattice that can trap excitons and magnons in specific locations. This "twistronics" approach could allow scientists to create arrays of quantum bits (qubits) within a single material, but the precision required for such manufacturing is currently at the limit of modern technology.
"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. "The goal of this article is to bring those developments into a coherent framework and identify where the field can go next."
As the CCNY team and their international collaborators continue to probe these materials, the boundaries of what is possible in quantum science continue to expand. The shift from separate "channels" of physics to a unified "quantum nexus" of light and magnetism suggests that the next era of technology will not just be smaller and faster, but fundamentally different in how it processes the world around us.
