February 17, 2026 by Ingrid Fadelli, Phys.org
Collected at: https://phys.org/news/2026-02-nanoengineers-chip-excitonic-hyperlens.html
When light passes through materials, it typically changes direction and bends in predictable ways. This change in direction, known as refraction, is caused by a change in the speed of light as it enters a new medium. In some rare cases, however, light bends differently, specifically in the opposite direction, and this is known as negative refraction. This unusual change in direction can be leveraged to develop a wide range of advanced technologies, including advanced imaging systems and small optical devices.
Researchers at the University of Hong Kong recently demonstrated negative diffraction in a magnetic semiconductor leveraging excitons (i.e., bound electron-hole pairs). Their paper, published in Nature Nanotechnology, also reports the development of an integrated nanophotonic chip that acts as a hyperlens, an optical component that can resolve extremely small details.
“Our research originated from a longstanding question: can light be manipulated in unconventional ways?” Jingwen Ma, first author of the paper, told Phys.org.
“This question has been one of the central pursuits of our group, led by Professor Xiang Zhang, for more than 20 years. Over the past two decades, the field has relied largely on plasmonic metamaterials—artificially engineered metallic nanostructures—to achieve unusual optical effects.”
Prof. Zhang’s team at the University of Hong Kong has been developing carefully nanoengineered metamaterials with unique qualities for years. While the structures they introduced in their earlier works were found to be promising for various applications, they also proved to be difficult to fabricate on a large scale.
“An inherent limitation of these structures is that they typically require feature sizes on the scale of tens of nanometers, making fabrication both difficult and expensive,” said Ma.
“This challenge led us to a simple yet fundamental question: could negative refraction—a phenomenon that normally requires meticulously patterned metamaterials—exist in a natural, unpatterned material? This question became the inspiration for this work, which was aimed at experimentally demonstrating such a possibility using an entirely intrinsic material mechanism.”
Negative refraction arising from a natural magnetic material
Ma and his colleagues observed negative diffraction in the layered magnetic semiconductor CrSBr. This material is known for its exceptionally strong excitonic response, which means that it strongly reacts to light or energy, producing excitons.
“In CrSBr, the internal magnetic moments are aligned along a well-defined direction,” explained Ma. “This magnetic order directly governs the behavior of excitons—quasiparticles formed by bound electron-hole pairs—and the way they propagate and re-emit light. We directed a beam of light into a thin flake of CrSBr placed on a dielectric substrate.”
The researchers observed that the excitons in CrSBr re-emitted light in a direction opposite to that of the incident beam (i.e., the light beam applied to the material). This is a clear signature of negative refraction.
“The on-chip excitonic hyperlens consists of a precisely cleaved slab of CrSBr integrated onto a photonic chip,” said Ma. “Light is coupled into the slab, and the excitons guide it along curved trajectories that converge into a spot comparable in size to the wavelength of light. This forms a hyperlens that operates entirely within a naturally occurring material.”
Potential applications and future research directions
Ma and his colleagues were the first to observe negative refraction driven by excitons in a natural magnetic material, without the need to carefully engineer it with patterning techniques. Their work introduces a new platform for controlling light at a nanoscale that could be used to develop innovative and advanced technologies.
“Our findings bridge two previously distinct fields—magnetism and nanophotonics—in a direct and material-intrinsic manner,” said Ma.
“From a practical perspective, it opens new possibilities for reconfigurable optical components. Because the magnetic order in CrSBr can be switched using an external magnetic field or by changing temperature, the same device can be toggled between normal and negative refraction.”
In the future, the material identified by the researchers could be used to create various new technologies that rely on negative refraction, including microscopy tools, high-resolution lithography techniques and optical computing systems. Meanwhile, Ma and his colleagues are continuing their work in this area, focusing on two main research directions.
“The first involves integrating CrSBr with other photonic and optoelectronic components to build functional prototype devices—such as a tunable superlens or a magnetic-field-controlled optical switch,” explained Ma.
“The second explores stacks of multiple CrSBr layers with small twist angles, where the resulting Moiré superlattice can dramatically alter exciton behavior. Looking ahead, we hope to develop this platform for studying the interactions between magnetism and photonics at the nanoscale.”
Publication details
Jingwen Ma et al, Excitonic negative refraction mediated by magnetic orders, Nature Nanotechnology (2026). DOI: 10.1038/s41565-025-02118-5.
Journal information: Nature Nanotechnology
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