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Ultrathin quantum light source with van der Waals NbOCl2 crystal

Nature volume 613, pages 53–59 (2023)Cite this article

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Abstract

Interlayer electronic coupling in two-dimensional materials enables tunable and emergent properties by stacking engineering. However, it also results in significant evolution of electronic structures and attenuation of excitonic effects in two-dimensional semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayers are stacked into van der Waals structures. Here we report a van der Waals crystal, niobium oxide dichloride (NbOCl2), featuring vanishing interlayer electronic coupling and monolayer-like excitonic behaviour in the bulk form, along with a scalable second-harmonic generation intensity of up to three orders higher than that in monolayer WS2. Notably, the strong second-order nonlinearity enables correlated parametric photon pair generation, through a spontaneous parametric down-conversion (SPDC) process, in flakes as thin as about 46 nm. To our knowledge, this is the first SPDC source unambiguously demonstrated in two-dimensional layered materials, and the thinnest SPDC source ever reported. Our work opens an avenue towards developing van der Waals material-based ultracompact on-chip SPDC sources as well as high-performance photon modulators in both classical and quantum optical technologies1,2,3,4.

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Fig. 1: Structural characterization.
Fig. 2: Weak interlayer electronic coupling.
Fig. 3: Anisotropic and scalable SHG response.
Fig. 4: Nonclassical parametric photon pair generation through SPDC.

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Data availability

All data supporting the findings of this study are available in the main text, Methods or Supplementary Information. The data are also available from the corresponding authors upon reasonable request.

References

  1. Elshaari, A. W., Pernice, W., Srinivasan, K., Benson, O. & Zwiller, V. Hybrid integrated quantum photonic circuits. Nat. Photon. 14, 285–298 (2020).

    Article  ADS  CAS  Google Scholar 

  2. Wang, Y., Jöns, K. D. & Sun, Z. Integrated photon-pair sources with nonlinear optics. Appl. Phys. Rev. 8, 011314 (2021).

    Article  ADS  CAS  Google Scholar 

  3. Li, L. et al. Metalens-array–based high-dimensional and multiphoton quantum source. Science 368, 1487–1490 (2020).

    Article  ADS  CAS  Google Scholar 

  4. Santiago-Cruz, T., Sultanov, V., Zhang, H., Krivitsky, L. A. & Chekhova, M. V. Entangled photons from subwavelength nonlinear films. Opt. Lett. 46, 653–656 (2021).

    Article  ADS  Google Scholar 

  5. Liu, Y., Huang, Y. & Duan, X. Van der Waals integration before and beyond two-dimensional materials. Nature 567, 323–333 (2019).

    Article  ADS  CAS  Google Scholar 

  6. Hong, H. et al. Giant enhancement of optical nonlinearity in two-dimensional materials by multiphoton-excitation resonance energy transfer from quantum dots. Nat. Photon. 15, 510–515 (2021).

    Article  ADS  CAS  Google Scholar 

  7. Wang, G. et al. Giant enhancement of the optical second-harmonic emission of WSe2 monolayers by laser excitation at exciton resonances. Phys. Rev. Lett. 114, 097403 (2015).

    Article  ADS  CAS  Google Scholar 

  8. Shi, J. et al. 3R MoS2 with broken inversion symmetry: a promising ultrathin nonlinear optical device. Adv. Mater. 29, 1701486 (2017).

    Article  Google Scholar 

  9. Adelwahab, I. et al. Giant second-harmonic generation in ferroelectric NbOI2. Nat. Photon. 16, 644–650 (2022).

    Article  ADS  Google Scholar 

  10. Marini, L., Helt, L. G., Lu, Y., Eggleton, B. J. & Palomba, S. Constraints on downconversion in atomically thick films. J. Opt. Soc. Am. B 35, 672 (2018).

    Article  ADS  CAS  Google Scholar 

  11. Dinparasti Saleh, H. et al. Towards spontaneous parametric down conversion from monolayer MoS2. Sci. Rep. 8, 3862 (2018).

    Article  ADS  Google Scholar 

  12. Kumar, N. et al. Second harmonic microscopy of monolayer MoS2. Phys. Rev. B 87, 161403 (2013).

    Article  ADS  Google Scholar 

  13. Li, Y. et al. Probing symmetry properties of few-layer MoS2 and h-BN by optical second-harmonic generation. Nano Lett. 13, 3329–3333 (2013).

    Article  ADS  CAS  Google Scholar 

  14. Le, C. T. et al. Effects of interlayer coupling and band offset on second harmonic generation in vertical MoS2/MoS2(1-x)Se2x structures. ACS Nano 14, 4366–4373 (2020).

    Article  CAS  Google Scholar 

  15. Zhang, J., Zhao, W., Yu, P., Yang, G. & Liu, Z. Second harmonic generation in 2D layered materials. 2D Mater. 7, 042002 (2020).

    Article  Google Scholar 

  16. Yu, J. et al. Giant nonlinear optical activity in two-dimensional palladium diselenide. Nat. Commun. 12, 1083 (2021).

    Article  ADS  CAS  Google Scholar 

  17. Song, Y. et al. Extraordinary second harmonic generation in ReS2 atomic crystals. ACS Photon. 5, 3485–3491 (2018).

    Article  CAS  Google Scholar 

  18. Hu, L. & Huang, X. Peculiar electronic, strong in-plane and out-of-plane second harmonic generation and piezoelectric properties of atom-thick α-M2X3 (M = Ga, In; X = S, Se): role of spontaneous electric dipole orientations. RSC Adv. 7, 55034–55043 (2017).

    Article  ADS  CAS  Google Scholar 

  19. Leuthold, J., Koos, C. & Freude, W. Nonlinear silicon photonics. Nat. Photon. 4, 535–544 (2010).

    Article  ADS  CAS  Google Scholar 

  20. Datta, I. et al. Low-loss composite photonic platform based on 2D semiconductor monolayers. Nat. Photon. 14, 256–262 (2020).

    Article  ADS  CAS  Google Scholar 

  21. Marino, G. et al. Spontaneous photon-pair generation from a dielectric nanoantenna. Optica 6, 1416 (2019).

    Article  ADS  CAS  Google Scholar 

  22. Hillebrecht, H. et al. Structural and scanning microscopy studies of layered compounds MCl3 (M = Mo, Ru, Cr) and MOCl2 (M =V, Nb, Mo, Ru, Os). J. Alloys Compd. 246, 70–79 (1997).

    Article  CAS  Google Scholar 

  23. Jia, Y., Zhao, M., Gou, G., Zeng, X. C. & Li, J. Niobium oxide dihalides NbOX2: a new family of two-dimensional van der Waals layered materials with intrinsic ferroelectricity and antiferroelectricity. Nanoscale Horiz. 4, 1113–1123 (2019).

    Article  ADS  CAS  Google Scholar 

  24. Polman, A., Kociak, M. & Garcia de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019).

    Article  ADS  CAS  Google Scholar 

  25. Li, L. et al. Direct observation of the layer-dependent electronic structure in phosphorene. Nat. Nanotechnol. 12, 21–25 (2017).

    Article  ADS  Google Scholar 

  26. Yang, Y. et al. Weak interlayer interaction in 2D anisotropic GeSe2. Adv. Sci. 6, 1801810 (2019).

    Article  Google Scholar 

  27. Garza, A. J. & Scuseria, G. E. Predicting band gaps with hybrid density functionals. J. Phys. Chem. Lett. 7, 4165–4170 (2016).

    Article  CAS  Google Scholar 

  28. Wang, X., Meng, W. & Yan, Y. Electronic band structures and excitonic properties of delafossites: a GW-BSE study. J. Appl. Phys. 122, 085104 (2017).

    Article  ADS  Google Scholar 

  29. Zhou, X. et al. Strong second-harmonic generation in atomic layered GaSe. J. Am. Chem. Soc. 137, 7994–7997 (2015).

    Article  CAS  Google Scholar 

  30. Yao, K. et al. Continuous wave sum frequency generation and imaging of monolayer and heterobilayer two-dimensional semiconductors. ACS Nano 14, 708–714 (2020).

    Article  CAS  Google Scholar 

  31. Wang, Y., Xiao, J., Yang, S., Wang, Y. & Zhang, X. Second harmonic generation spectroscopy on two-dimensional materials [Invited]. Opt. Mater. Express 9, 1136–1149 (2019).

    Article  ADS  Google Scholar 

  32. Wu, Q., Hewitt, T. D. & Zhang, X.-C. Two-dimensional electro-optic imaging of THz beams. Appl. Phys. Lett. 69, 1026–1028 (1996).

    Article  ADS  CAS  Google Scholar 

  33. Platonov, A. V., Kochereshko, V. P., Ivchenko, E. L. & Mikhailov, G. V. Giant electro-optical anisotropy in type-II heterostructures. Phys. Rev. Lett. 83, 3546–3549 (1999).

    Article  ADS  CAS  Google Scholar 

  34. Ribeiro-Soares, J. et al. Second harmonic generation in WSe2. 2D Mater. 2, 045015 (2015).

    Article  Google Scholar 

  35. Autere, A. et al. Nonlinear optics with 2D layered materials. Adv. Mater. 30, 1705963 (2018).

    Article  Google Scholar 

  36. Okoth, C., Cavanna, A., Santiago-Cruz, T. & Chekhova, M. V. Microscale generation of entangled photons without momentum conservation. Phys. Rev. Lett. 123, 263602 (2019).

    Article  ADS  CAS  Google Scholar 

  37. Trovatello, C. et al. Optical parametric amplification by monolayer transition metal dichalcogenides. Nat. Photon. 15, 6–10 (2020).

    Article  ADS  Google Scholar 

  38. Santiago-Cruz, T. et al. Photon pairs from resonant metasurfaces. Nano Lett. 21, 4423–4429 (2021).

    Article  ADS  CAS  Google Scholar 

  39. Hu, G. et al. Topological polaritons and photonic magic angles in twisted α-MoO3 bilayers. Nature 582, 209–213 (2020).

    Article  ADS  CAS  Google Scholar 

  40. Andrei, E. Y. & MacDonald, A. H. Graphene bilayers with a twist. Nat. Mater. 19, 1265–1275 (2020).

    Article  ADS  CAS  Google Scholar 

  41. Peña, F. D. L. et al. hyperspy/hyperspy: release v1.6.5 (v1.6.5). Zenodo https://doi.org/10.5281/zenodo.5608741 (2021).

  42. Mao, H. K., Xu, J. & Bell, P. M. Calibration of the ruby pressure gauge to 800 kbar under quasihydrostatic conditions. J. Geophys. Res. 91, 4673–4676 (1986).

    Article  ADS  CAS  Google Scholar 

  43. Kresse, G., Furthmüller, J., Furthmuller, J. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).

    Article  ADS  CAS  Google Scholar 

  44. Heyd, J., Scuseria, G. E. & Ernzerhof, M. Hybrid functionals based on a screened coulomb potential. J. Chem. Phys. 118, 8207–8215 (2003).

    Article  ADS  CAS  Google Scholar 

  45. Peralta, J. E., Heyd, J., Scuseria, G. E. & Martin, R. L. Spin-orbit splittings and energy band gaps calculated with the Heyd-Scuseria-Ernzerhof screened hybrid functional. Phys. Rev. B 74, 073101 (2006).

    Article  ADS  Google Scholar 

  46. Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

    Article  ADS  CAS  Google Scholar 

  47. VASP_TDM GitHub https://github.com/QijingZheng/VASP_TDM (2016).

  48. Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).

    Article  Google Scholar 

  49. Perdew, J. P. & Zunger, A. Self-interaction correction to density-functional approximations for many-electron systems. Phys. Rev. B 23, 5048–5079 (1981).

    Article  ADS  CAS  Google Scholar 

  50. van Setten, M. J. et al. The PseudoDojo: training and grading a 85 element optimized norm-conserving pseudopotential table. Comput. Phys. Commun. 226, 39–54 (2018).

    Article  ADS  Google Scholar 

  51. Hamann, D. R. Optimized norm-conserving Vanderbilt pseudopotentials. Phys. Rev. B 88, 085117 (2013).

    Article  ADS  Google Scholar 

  52. Lazzeri, M. & Mauri, F. First-principles calculation of vibrational Raman spectra in large systems: signature of small rings in crystalline SiO2. Phys. Rev. Lett. 90, 036401 (2003).

    Article  ADS  Google Scholar 

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Acknowledgements

Q.G., S.J.P. and A.T.S.W. acknowledge financial support from the Ministry of Education Tier 2 grant MOE2017-T2-2-139. Q.G. sincerely thanks Q. Zhang, K. Zheng and G. Xu for help with chemicals and furnace facilities for crystal synthesis and X-ray diffraction measurements. Q.G. sincerely thanks M. Li for valuable discussions. Q.G. thanks M. Wu, Y. Yu and J. Dan for help with STEM. X.-F.R. and G.-C.G. acknowledge financial support of the Innovation Program for Quantum Science and Technology (grant number 2021ZD0303200), the National Natural Science Foundation of China (grant numbers 61590932, 11774333, 62061160487 and 12004373), the Anhui Initiative in Quantum Information Technologies (grant number AHY130300) and the Strategic Priority Research Program of the Chinese Academy of Sciences (grant number XDB24030601). This work was partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication. The work at University of Chinese Academy of Sciences was financially supported by the National Key R&D Program of China (2018YFA0305800) and the Beijing Outstanding Young Scientist Program (BJJWZYJH01201914430039). C.-W.Q. acknowledges the financial support of the National Research Foundation, Prime Minister’s Office, Singapore under Competitive Research Program Award NRF-CRP26-2021-0004. H.G. acknowledges the financial support of the National Science Fund for Distinguished Young Scholars (grant number T2225027). Z.X. acknowledges the financial support of the National National Science Foundation of China (grant number 51972130). X.Z. acknowledges the financial support of the Peking University startup funding and the National Natural Science Foundation of China (grant number 52273279).

Author information

Author notes

  1. These authors contributed equally: Qiangbing Guo, Xiao-Zhuo Qi, Lishu Zhang, Meng Gao

Authors and Affiliations

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

    Qiangbing Guo, Wenjie Zang & Cheng-Wei Qiu

  2. Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore

    Qiangbing Guo & Stephen J. Pennycook

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

    Qiangbing Guo, Junyong Wang, Goki Eda, Yuan Ping Feng, Cheng-Wei Qiu & Andrew T. S. Wee

  4. CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, China

    Xiao-Zhuo Qi, Yun-Kun Wu, Guang-Can Guo & Xi-Feng Ren

  5. CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, China

    Xiao-Zhuo Qi, Yun-Kun Wu, Guang-Can Guo & Xi-Feng Ren

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

    Lishu Zhang, Junyong Wang, Goki Eda, Yuan Ping Feng & Andrew T. S. Wee

  7. School of Physical Sciences and CAS Key Laboratory of Vacuum Physics, University of Chinese Academy of Sciences, Beijing, China

    Meng Gao, Mingquan Xu, Wu Zhou & Stephen J. Pennycook

  8. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China

    Sanlue Hu & Zewen Xiao

  9. Center for High Pressure Science and Technology Advanced Research, Beijing, China

    Wenju Zhou, Bingmin Yan & Huiyang Gou

  10. School of Materials Science and Engineering, Peking University, Beijing, China

    Xiaoxu Zhao

  11. Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore, Singapore

    Shengyuan A. Yang

  12. Hefei National Laboratory, University of Science and Technology of China, Hefei, China

    Guang-Can Guo & Xi-Feng Ren

  13. CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, China

    Wu Zhou

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  1. Qiangbing Guo
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Contributions

Q.G. conceived the ideas, designed the experiments and organized the research project under the supervision of A.T.S.W., S.J.P. and C.-W.Q. Q.G. synthesized the crystals and prepared all samples for the experiments. Q.G., J.W., B.Y., Wenju Zhou, G.E. and H.G. measured Raman spectra. M.G., W. Zang., X.Z., M.X., Wu Zhou and S.J.P. carried out STEM-related characterization techniques. X.-Z.Q., Q.G., Y.-K.W., X.-F.R. and G.-C.G. designed and conducted the harmonic generation and parametric down-conversion experiments. S.H., L.Z., Z.X. and Y.P.F. carried out the theoretical calculations. S.A.Y. provided theoretical support in revision. Q.G. analysed the data and drafted the manuscript with input from all authors. Q.G., C.-W.Q., X.-F.R., S.J.P. and A.T.S.W. provided major revisions. All authors discussed the results and contributed to the manuscript.

Corresponding authors

Correspondence to Qiangbing Guo, Xi-Feng Ren, Cheng-Wei Qiu, Stephen J. Pennycook or Andrew T. S. Wee.

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Supplementary Information

This file includes Supplementary Sections 1–7, Figs. 1–29, Tables 1–4 and References. Further information and data on structural characterization, electronic structure and optical transition analysis, interlayer properties, lattice vibrational properties, SHG and SPDC are listed.

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Guo, Q., Qi, XZ., Zhang, L. et al. Ultrathin quantum light source with van der Waals NbOCl2 crystal. Nature 613, 53–59 (2023). https://doi.org/10.1038/s41586-022-05393-7

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