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Chin. Phys. B, 2026, Vol. 35(5): 057802    DOI: 10.1088/1674-1056/ae12d8
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES Prev  

Tunable multi-frequency exceptional points in non-Hermitian terahertz metasurfaces

Xiang Hou(侯翔), Fangze Deng(邓方泽), Zhihua Han(韩志华), Yumeng Ma(马宇萌), Chenglong Wang(王成龙), Yuchao Li(李玉超), Keke Cheng(程可可), Ke Ma(马克), Yansheng Shao(邵延胜), Ruidan Zhou(周瑞丹), Yuping Zhang(张玉萍), Meng Liu(刘蒙), and Huiyun Zhang(张会云)
Qingdao Key Laboratory of Terahertz Technology, College of Electronic and Information Engineering, Shandong University of Science and Technology, Qingdao 266590, China
Abstract  Exceptional points (EPs) in non-Hermitian metasurfaces have garnered considerable attention due to their unique advantages in cutting-edge applications such as ultra-sensitive sensing and unidirectional reflectionlessness. However, existing studies on metasurfaces employing both active and passive tuning mechanisms can only observe a single EP, which fails to meet the requirements for multi-frequency responses or multifunctional integration, thus limiting the enhancement of device performance. In this study, we design a terahertz (THz) non-Hermitian metasurface device that is actively tuned by the phase-change material VO$_{2}$. By keeping the geometric dimensions of the device unchanged, we achieve the simultaneous induction and detection of multi-frequency EPs at multiple frequency points. Through the regulation of VO$_{2}$ conductivity, the gain-loss distribution of the system can be continuously controlled, leading to the degeneracy of eigenvalues and eigenstates across multiple discrete frequency bands, thereby forming multi-frequency EPs. Furthermore, the design of chiral structures demonstrates that, under identical conductivity conditions, the eigenstates of the original metasurface structure and its chiral counterpart can degenerate into circularly polarized states with opposite rotations, enabling the switching of polarization chirality. These results illustrate that the deep integration of phase-change materials, non-Hermitian photonics, and electromagnetic manipulation in metasurfaces provides a novel design paradigm for the dynamic regulation of multi-frequency EPs and circular polarization control, laying a foundation for the development of high-performance and multifunctional integrated photonic platforms in the THz regime.
Keywords:  exceptional points      terahertz      non-Hermitian      metasurfaces  
Received:  21 August 2025      Revised:  07 October 2025      Accepted manuscript online:  14 October 2025
PACS:  78.67.Pt (Multilayers; superlattices; photonic structures; metamaterials)  
  42.25.Ja (Polarization)  
Fund: This work was supported by the National Natural Science Foundation of China (Grant No. 62375158), the Qingdao Natural Science Foundation (Grant No. 25-1-1-153-zyydjch), and the Development Plan of Youth Innovation Team in Colleges and Universities of Shandong Province (Grant No. 2022KJ216).
Corresponding Authors:  Meng Liu, Huiyun Zhang     E-mail:  liumeng@sdust.edu.cn;sdust_thz@126.com

Cite this article: 

Xiang Hou(侯翔), Fangze Deng(邓方泽), Zhihua Han(韩志华), Yumeng Ma(马宇萌), Chenglong Wang(王成龙), Yuchao Li(李玉超), Keke Cheng(程可可), Ke Ma(马克), Yansheng Shao(邵延胜), Ruidan Zhou(周瑞丹), Yuping Zhang(张玉萍), Meng Liu(刘蒙), and Huiyun Zhang(张会云) Tunable multi-frequency exceptional points in non-Hermitian terahertz metasurfaces 2026 Chin. Phys. B 35 057802

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