Concept of magnetic order-mediated excitonic negative refraction and schematic of the micro-device.
Imagine shining a flashlight into a material and watching the light bend backward – or in an entirely unexpected direction – as if defying the law of physics. This phenomenon, known as negative refraction, could transform imaging, telecommunications, and countless other technologies.
Now, a team of scientists led by Academician Professor Xiang Zhang, President and Vice-Chancellor of The University of Hong Kong (HKU) and Chair of Engineering and Physics, has made a major breakthrough by using a natural magnetic material called CrSBr to achieve negative refraction — without the need for complicated artificial structures. This discovery opens the door to ultra-compact lenses, super-high-resolution microscopes, and reconfigurable optical devices that can be controlled with magnets.
How They Did It
The researchers used a very thin layer of CrSBr, a material that has a unique magnetic structure—its magnetic atoms align in different ways within and between layers. This magnetic order changes how the material interacts with light. When the magnetic order is active, it causes light to bend "the wrong way," creating negative refraction.
By guiding light into this material on a tiny chip, the team visually confirmed the backward bending of light. They also built a miniature "hyperlens"—a device that can focus light into extremely small spots—an essential step for future high-precision imaging and data processing.
Why It Matters
Traditional materials that bend light this way are often complex and difficult to control. Using natural magnetic materials like CrSBr means easier, more flexible control of light at the nanoscale. Plus, the device can be turned on and off with magnets or changes in temperature, paving the way for smarter, reprogrammable optical systems.
Leading Researchers and Support
This pioneering work was led by Professor Zhang and carried out by Research Assistant Professor Jingwen Ma and Postdoctoral Fellow Xiong Wang from HKU, in collaboration with Professor Xiaoze Liu from Wuhan University and Professor Zuxin Chen from South China Normal University. Professors Cui Xiaodong, Yin Xiaobo, and Zhang Shuang from HKU's State Key Laboratory of Optical Quantum Materials also provided significant guidance.
Future Outlook
This discovery provides a foundation for next-generation technologies such as highly detailed medical imaging, advanced manufacturing, and quantum computing. It also supports Hong Kong's ambitions to lead in high-tech innovation and quantum technologies—areas vital for regional development.
About the Research and Acknowledgments
Supported by grants from the Hong Kong Research Grants Council (N_HKU750/22, 17208725) and the National Natural Science Foundation of China (62261160386, 62104073), this research underscores Hong Kong's strength in cutting-edge science and innovation. The research team thanks Professor Liu Zhaowei of the University of California, San Diego, Professor Dong Jianwen of Sun Yat-sen University, and Professor Guo Xiangdong of Shanghai Jiao Tong University for fruitful discussions, as well as the relevant teams at The University of Hong Kong for their support in nanofabrication. By harnessing the magnetic properties of naturally occurring materials, the team has opened exciting new possibilities for controlling light at the tiniest scales.
Link to paper:
Jingwen Ma, Xiong Wang, Yuanhao Gong, et al. "Excitonic negative refraction mediated by magnetic orders." Nature Nanotechnology (2026)
