Quantum Breakthrough Unites Light and Magnetism in Atomically Thin Materials

For decades, scientists have struggled to unify the optical properties of semiconductors with magnetism. Now, researchers at the City College of New York (CCNY) have mapped a new frontier in atomically thin quantum materials where light, electric charge, and magnetism are intrinsically linked. The research, emerging from physicist Vinod M. Menon's Laboratory for Nano and Micro Photonics (LaNMP), demonstrates that these unusual interactions could serve as the foundation for advanced optoelectronic devices that manipulate light, charge, and electron spin simultaneously.

Detailed in a comprehensive review published in the journal Nature Materials, the study focuses on van der Waals magnetic semiconductors. Historically, scientists attempted to merge these properties by adding magnetic atoms to semiconductors or stacking thin semiconductors on top of magnetic layers. However, van der Waals crystals offer a direct solution: within these materials, light-generated excitations known as excitons and magnetic moments emerge from the exact same electronic orbitals.

When incoming light energizes an electron, it moves and leaves behind a positively charged "hole." This linked electron-hole pair forms an exciton, an electrically neutral particle that interacts strongly with light. Meanwhile, magnons are collective waves traveling through a material's organized magnetic structure. In these newly analyzed two-dimensional magnets - specifically chromium triiodide, nickel phosphorus trisulfide, and chromium sulfur bromide - excitons and magnons directly influence each other.

In these materials, light and magnetism no longer operate as separate channels. 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.

- Pratap Chandra Adak, City College of New York

This shared origin allows excitons to significantly strengthen magneto-optical effects, enabling scientists to read magnetic states simply by observing changes in light polarization. Conversely, the magnetic order can alter the energy of excitons and dictate where they are confined within the crystal. The researchers also highlighted exciton polaritons - hybrid particles combining light and matter - that can transport optical information seamlessly through the 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," Menon explained. He noted that the primary goal of their review is to bring these rapid developments into a coherent framework and identify the field's future trajectory.

The ability to precisely control light and magnetism at microscopic scales opens the door to several theoretical applications. The CCNY team identified potential breakthroughs in magneto-photonic memory, data readout systems, all-optical logic gates, adjustable light-emitting devices, and magneto-optic lasers. One of the most promising applications lies in quantum transducers - devices capable of converting signals between microwave and optical frequencies.

Despite these advancements, the researchers caution that the field remains largely unexplored. Scientists still lack comprehensive theoretical models capable of predicting how excitons, electron spins, lattice vibrations, and photons behave during simultaneous interaction. Future research will need to investigate complex phenomena like moiré magnetic excitons, the optical control of spin textures, and magnetic exciton polariton condensation.

The review represents a massive collaborative effort, featuring co-authors 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 foundational work at CCNY was heavily supported by funding from DARPA and the Gordon and Betty Moore Foundation.

The most critical revelation in this research isn't just the manipulation of light and magnetism - it is the specific mention of quantum transducers. Currently, the world's most powerful superconducting quantum computers operate at microwave frequencies and must be isolated inside massive cryogenic refrigerators. To build a true, global quantum internet, those fragile microwave signals must be converted into optical frequencies so they can travel through standard fiber-optic cables without losing their quantum state.

By proving that van der Waals magnetic semiconductors can bridge optical signals with magnetic activity at gigahertz frequencies, the CCNY team has essentially identified a potential hardware solution for this exact bottleneck. If engineers can harness these atomically thin quantum materials to build efficient, scalable quantum transducers, it will mark the transition of quantum computing from isolated laboratory mainframes to a globally connected, high-speed network.