Recent advancements in nanophotonics are moving beyond isotropic noble metals to achieve dynamic and directional control over plasmons. Conventional localized surface plasmon resonances (LSPR) are limited by their isotropic permittivity and geometry-dependent resonance tuning. Introducing strong material anisotropy offers an effective alternative strategy, providing an additional degree of freedom for controlling plasmon propagation and confinement.
To address this gap, a team of researchers has demonstrated hyperbolic localized plasmon resonances in an anisotropic two-dimensional crystal. The research was an outcome of an international collaborative effort. Special Appointment Professor Hiroaki Misawa from the Research Institute for Interdisciplinary Science, Advanced Research Field, Okayama University, who led the research, was joined by Dr. Yaolong Li from the Research Institute for Electronic Science, Hokkaido University; Xu Shi from the Institute for Integrated Innovations, Hokkaido University; Yasutaka Matsuo from the Institute for Integrated Innovations, Hokkaido University; and Qihuang Gong from the State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing, China. The key to success was the exceptionally well-coordinated integration of state-of-the-art nanofabrication facilities, advanced measurement and characterization platforms, and complementary human expertise across the three institutions. The details of the study were published in Nature Communications on February 13, 2026.
Speaking about the motivation behind this study, Prof. Misawa explained, “Conventional plasmonic platforms, largely based on isotropic noble metals, offer limited intrinsic anisotropy, making it difficult to achieve robust, controllable chirality and tunable field confinement. It has also remained unclear how hyperbolic dispersion manifests as localized plasmon resonances. Therefore, we turned to the strongly in-plane anisotropic layered crystal MoOCl₂ to experimentally establish hyperbolic localized plasmon resonances (H-LPRs) and to open a new design handle, twist stacking, for engineering optical chirality.”
MoOCl 2 is a layered van der Waals crystal with a monoclinic structure that exhibits pronounced in-plane anisotropy. It behaves metallically along one crystallographic axis while remaining dielectric in the perpendicular direction. This optical contrast leads to hyperbolic dispersion, with light propagation in directional patterns.
When patterned into circular nanodisks, MoOCl₂ displayed localized plasmon resonances only for light polarized along the metallic axis, confirming the one-dimensional nature of these modes arising from the material’s anisotropic permittivity. Near-field imaging further verified this anisotropic behavior, revealing volumetric electromagnetic field distributions that differ significantly from those observed in conventional plasmonic systems.
In vertically stacked MoOCl 2 /Al 2 O 3 /Au metal-insulator-metal structures, the plasmon resonance wavelength remained nearly unchanged even when the separation between layers (Z-gap) varied. This behavior demonstrates that the Z-gap independence is an intrinsic property of MoOCl₂ H-LPRs, highlighting their robustness for device integration.
Moreover, by stacking identical MoOCl₂ disks with a controlled twist, the team achieved significant optical chirality without breaking geometric symmetry. The maximum circular dichroism exceeded 0.65 in simulations and reached 0.54 in experiments, which was achieved through the increased density and stronger near-field coupling between adjacent disks.
By leveraging strongly confined hyperbolic fields and twist-induced chirality, this research could enable miniaturized photonic components, such as ultra-compact polarization and chiral-optics devices, including tunable circular dichroism filters, chiral modulators, and polarization converters. The technology could also be utilized for high-sensitivity sensors required for molecular fingerprinting and enantiomer-selective detection in chemistry or biomedicine.
“Our findings open a pathway to highly integrated, nanoscale photonic functionality, potentially in the mid-infrared/THz, a spectral range that is essential for molecular fingerprint sensing. Existing optical components in this range are frequently large and complicated. Our findings can help in the development of compact, low-power, high-sensitivity spectroscopic sensors for quick and highly selective detection of chiral molecules. These can be utilized for quality control and safety or health applications. Thus, it can impact the chemical, pharmaceutical, biomedical, environmental monitoring, and semiconductor or photonics industries. Crucially, our method lessens reliance on intricate 3D nanofabrication and reduces constraints in manufacturability, scalability, and reproducibility ,” concluded Prof. Misawa.
About Okayama University, Japan
As one of the leading universities in Japan, Okayama University aims to create and establish a new paradigm for the sustainable development of the world. Okayama University offers a wide range of academic fields, which become the basis of the integrated graduate schools. This not only allows us to conduct the most advanced and up-to-date research, but also provides an enriching educational experience.
Website: https://www.okayama-u.ac.jp/index_e.html
About Special Appointment Professor Hiroaki Misawa from Okayama University, Japan
Dr. Hiroaki Misawa is a Special Appointment Professor at Okayama University. He is known for his pioneering work in photochemistry, plasmonics, and nanophotonics. He earned his Ph.D. in chemistry from the University of Tsukuba in 1984. His research explores light-matter interactions, plasmon-induced chemical reactions, and nanostructured materials for energy conversion and artificial photosynthesis. Dr. Misawa has authored more than 500 scientific publications and has significantly advanced the field of plasmonic chemistry. His work has contributed to new approaches for solar energy conversion, photocatalysis, and nanoscale photonic technologies, earning him international recognition in materials science and photochemical research.
Nature Communications
Experimental study
Not applicable
Hyperbolic localized plasmons and twist-induced chirality in an anisotropic 2D material
13-Feb-2026
All authors declare that they have no competing interests.