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Colossal in-plane optical anisotropy in a two-dimensional van der Waals crystal

Nature Photonics (2024)Cite this article

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Abstract

Polarization, a fundamental property of light, has been widely exploited from quantum physics to high-dimensional optics. Materials with intrinsic optical anisotropy, such as dichroism and birefringence, are central to light polarization control, including the development of polarizers, waveplates, mirrors and phase-matching elements. Therefore, materials with strong optical anisotropy have been long-sought. Recently, two-dimensional van der Waals crystals show high optical anisotropy but are mostly restricted to the out-of-plane direction, which is challenging to access in optical engineering. Here we report a two-dimensional van der Waals material, NbOCl2, that exhibits sharp electronic and structural contrast between its in-plane orthogonal axes. Colossal in-plane optical anisotropy—linear dichroism (up to 99% in ultraviolet) and birefringence (0.26–0.46 within a wide visible–near-infrared transparency window)—is experimentally demonstrated. Our findings provide a powerful and easy-to-access recipe for ultracompact integrated polarization industries.

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Fig. 1: Optical anisotropy in 2D vdW crystals: in-plane versus out-of-plane anisotropy.
Fig. 2: Structure and in-plane LD of NbOCl2.
Fig. 3: In-plane optical constants and birefringence of NbOCl2.
Fig. 4: In-depth investigations of the large in-plane dielectric anisotropy.

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All relevant data are available in the main text, in the Supporting Information or from the authors upon reasonable request.

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Acknowledgements

This work is financially supported by the National Research Foundation, Prime Minister’s Office, Singapore, under Competitive Research Program Award NRF-CRP26-2021-0004 and NRF-CRP22-2019-0006, and by a grant (A-8002152-00-00) from the Ministry of Education, Singapore. Q.G. thanks W. Zang and S. J. Pennycook and for support with STEM. Q.G. thanks Q. Zhao, C. Shen and Y. Nie from Ideaoptics Inc. for help with microspectroscopy measurements. Q.G. thanks S. Hu and L. Zhang for helpful discussions. Q.G. thanks H. Wang for optical measurements. Q.G. and C.-W.Q. thank P. Zhu and M. Ren for help with optical measurements. Q.G. and C.-W.Q. thank J. Zhao, Q. Zheng and X. Tian for helpful discussions. Q.Z. acknowledges the financial support from the Research Funds of Hangzhou Institute for Advanced Study, UCAS (A05006C019014 and B03006C01600407), and Zhejiang Provincial Natural Science Foundation (grant number LQ24H180008).

Author information

Author notes

  1. These authors contributed equally: Qiangbing Guo, Qiuhong Zhang.

Authors and Affiliations

  1. Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore

    Qiangbing Guo, Tan Zhang & Cheng-Wei Qiu

  2. Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore

    Qiangbing Guo & Cheng-Wei Qiu

  3. School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China

    Qiuhong Zhang

  4. Institute of Materials Research and Engineering, A*STAR (Agency for Science Technology and Research), Singapore, Singapore

    Jun Zhou & Shijie Wang

  5. Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System, Harbin Institute of Technology (Shenzhen), Shenzhen, China

    Shumin Xiao

  6. Department of Physics, National University of Singapore, Singapore, Singapore

    Yuan Ping Feng

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Contributions

Q.G. and C.-W.Q. conceived and coordinated this work. Q.G. and Q.Z. synthesized the crystals and measured the optical transmission and reflection spectra. Q.G. and T.Z. calculated and extracted the optical constants. J.Z. and Y.P.F. did the theoretical calculations. Q.G. analysed the data and wrote the paper with revision from C.-W.Q. All authors discussed the results and contributed to the paper. Q.G. and C.-W.Q. supervised the project.

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Correspondence to Qiangbing Guo or Cheng-Wei Qiu.

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Nature Photonics thanks Yuanmu Yang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Guo, Q., Zhang, Q., Zhang, T. et al. Colossal in-plane optical anisotropy in a two-dimensional van der Waals crystal. Nat. Photon. (2024). https://doi.org/10.1038/s41566-024-01501-3

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