Metallic nanostructures are exceptionally effective at concentrating light into tiny volumes, while dielectric nanostructures excel at storing light with minimal energy loss. Combining these complementary properties has traditionally required complicated hybrid structures in which the two optical modes become mixed, making them difficult to control independently. Achieving both resonance types within a single nanostructure without mode interference has therefore remained a major challenge in nanophotonics, limiting the development of compact, multifunctional optical devices.
Addressing this challenge, a research team led by Special Appointment Professor Hiroaki Misawa from the Research Institute for Interdisciplinary Science, Advanced Research Field, Okayama University, Japan, along with Professor Qihuang Gong and Dr. Yaolong Li from Hokkaido University, Japan, and Peking University, China, and Dr. Xu Shi and Professor Yasutaka Matsuo from Hokkaido University, Japan, developed nanostructures using the naturally hyperbolic two-dimensional material MoOCl₂. Unlike conventional materials, MoOCl₂ behaves as a metal along one crystal direction and as a dielectric along the perpendicular direction, allowing two fundamentally different resonance modes to coexist within a single nanostructure. The study was first published online on June 20, 2026, and appeared in Volume 20, Issue 26 of ACS Nano on July 7, 2026.
The researchers fabricated arrays of MoOCl₂ nanodisks on a gold reflective film and investigated their optical behavior using spectroscopy, finite-difference time-domain simulations, and photoemission electron microscopy. The gold film acts as a mirror that enhances confinement of the dielectric mode while preserving the plasmonic mode. Their analysis revealed that x-polarized light excites a localized plasmon resonance along the material's metallic axis, whereas y-polarized light selectively excites a dielectric magnetic dipole resonance along the orthogonal dielectric axis. Because these modes originate from different crystal directions, they remain nonhybrid and can be independently controlled without mode mixing or crosstalk.
The two resonances also displayed strikingly different optical characteristics. The dielectric resonance exhibited a much higher quality factor, reaching 45.3 in experiments, approximately 5.7 times greater than that of the plasmonic resonance. By adjusting the nanostructure geometry, the researchers successfully tuned both resonances to overlap at the same wavelength while preserving independent polarization control. Photoemission electron microscopy further revealed that the dielectric resonance produced a nearly 300-fold stronger photoemission signal than the plasmonic mode, reflecting the different hotspot locations of the two resonances within the nanostructure.
"We wanted to independently control the light-concentrating function of metallic nanostructures and the light-trapping function of dielectric nanostructures within a single structure," explains Prof. Misawa. "MoOCl₂ offered this unique opportunity because its optical response changes with crystal direction, allowing two completely different resonance modes to coexist without interfering with each other."
The ability to switch between two independent resonances simply by rotating the polarization of incident light could simplify the design of highly integrated optical components. The researchers envision applications in highly sensitive optical and chemical sensors, ultra-compact optical switches, optical communication systems, optical information processing, nonlinear optical devices, and multifunctional metasurfaces capable of controlling light reflection, polarization, and propagation with unprecedented flexibility.
"This work provides a new design strategy for multifunctional nanophotonic devices using a single nanostructure instead of complicated hybrid systems," Prof. Misawa adds. "Such simplified architectures could support future photonic technologies that require precise, polarization-selective control of light."
Overall, the discovery that a single MoOCl₂ nanostructure can independently host metallic and dielectric resonance modes establishes a new platform for nanophotonic engineering. By exploiting the material's intrinsic metal-dielectric duality rather than combining different materials, the approach enables compact optical components with independently addressable functionalities, offering promising opportunities for next-generation sensing, optical communication, nonlinear photonics, and multifunctional metasurface technologies.
Reference
Title of original paper: Coexistence of Metal and Dielectric Resonance Modes in a Single Nanostructure of a Hyperbolic Material
Journal: ACS Nano
DOI: https://doi.org/10.1021/acsnano.6c06696
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 Professor Hiroaki Misawa from Okayama University, Japan
Prof. Hiroaki Misawa is a Special Appointment Professor at the Research Institute for Interdisciplinary Science, Advanced Research Field, Okayama University, Japan. He earned his D.Sc. degree from the University of Tsukuba in 1984. His research spans plasmonics, photochemistry, nanotechnology, fundamental physical chemistry, and applied condensed matter physics. A member of the Japanese Photochemistry Association, he serves as Editor-in-Chief of Journal of Photochemistry and Photobiology C: Photochemistry Reviews. With more than 20,449 citations and an h-index of 75, he is internationally recognized for advancing innovative materials and photochemical sciences. His pioneering work continues to inspire next-generation sustainable energy research.
Funding information
This research was supported by the National Key Research and Development Program of China (Grant Nos. 2024YFA1209201 and 2024YFA1209204), the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Nos. JP23H05464 and JP23K04902), the JSPS Program for Forming Japan's Peak Research Universities (J-PEAKS; Grant No. JPJS00420230010), the National Natural Science Foundation of China (Grant Nos. 12474322, 92250305, 12574405, and 12274008), the Quantum Science and Technology-National Science and Technology Major Project (Grant No. 2021ZD0301500), the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (Grant No. JYB2025XDXM106), and the Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT; Grant Nos. JPMXP1224HK0165 and JPMXP1225HK0063).
