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Strongly enhanced light–matter coupling of monolayer WS2 from a bound state in the continuum


Exciton–polaritons derived from the strong light–matter interaction of an optical bound state in the continuum with an excitonic resonance can inherit an ultralong radiative lifetime and significant nonlinearities, but their realization in two-dimensional semiconductors remains challenging at room temperature. Here we show strong light–matter interaction enhancement and large exciton–polariton nonlinearities at room temperature by coupling monolayer tungsten disulfide excitons to a topologically protected bound state in the continuum moulded by a one-dimensional photonic crystal, and optimizing for the electric-field strength at the monolayer position through Bloch surface wave confinement. By a structured optimization approach, the coupling with the active material is maximized here in a fully open architecture, allowing to achieve a 100 meV photonic bandgap with the bound state in the continuum in a local energy minimum and a Rabi splitting of 70 meV, which results in very high cooperativity. Our architecture paves the way to a class of polariton devices based on topologically protected and highly interacting bound states in the continuum.

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Fig. 1: Overall device architecture and energy–momentum dispersions.
Fig. 2: PL measurements and polariton BIC.
Fig. 3: Nonlinear shift of the polariton BIC.
Fig. 4: Topological nature of polariton BIC and its replicas.

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

Code availability

The codes used in this work are available from the corresponding authors upon request.


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We are grateful to C. Anton-Solanas for the fruitful discussions and for the help in the optimization of the fabrication process. We gratefully thank P. Cazzato for technical support, L. Dominici for fruitful discussions on the design solutions and L. Carbone for precious support in the development of the fabrication process. We acknowledge the CINECA award under the ISCRA C initiative (D.G. and E.M.) for the availability of high-performance computing resources and support. This work was supported by the Italian Ministry of University (MIUR) for funding through the PRIN project ‘Interacting photons in polariton circuits’—INPhoPOL (grant 2017P9FJBS) (D.S. and D.G.); the project ‘Hardware implementation of a polariton neural network for neuromorphic computing’—Joint Bilateral Agreement CNR-RFBR (Russian Foundation for Basic Research)—Triennal Program 2021–2023 (D.S.); the MIUR project ‘ECOTEC—eco-sustainable and intelligent fibers and fabrics for technic clothing’, PON R&I 2014-2020, project no. ARS0100951, CUP B66C18000300005 (V.M.); the Italian Ministry of Research (MUR) under the complementary actions to the NRRP (PNC0000007) ‘Fit4MedRob—Fit for Medical Robotics’ (grant-contract number CUP B53C22006960001) (V.M.); the MAECI project ‘Novel photonic platform for neuromorphic computing’, Joint Bilateral Project Italia–Polonia, 2022–2023 (D.S.); the PNRR MUR project ‘National Quantum Science and Technology Institute’ (NQSTI) (D.S. and D.G.); the PNRR MUR project: European Union—NextGeneration EU, ‘Integrated infrastructure initiative in photonic and quantum sciences’—I-PHOQS IR0000016, ID D2B8D520, CUP B53C22001750006 (D.S.); and the project ‘TECNOMED—Tecnopolo di Nanotecnologia e Fotonica per la Medicina di Precisione’ (MIUR Decreto Direttoriale no. 3449 del 4/12/2017, CUP B83B17000010001) (G.G.).

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E.M., L.P., F.T. and A.D.R. realized the samples. E.M. and D.B. conceived the idea. E.M. developed the nanofabrication process, numerical tools and theory/data analysis. L.P. performed the optical measurements. E.M., L.P., D.B., D.G. and D.S. wrote the text. A.C., M.P. and V.M. grew the dielectric mirrors. B.H. and C.S. contributed the exfoliated TMDs and mirrors for preliminary fabrication tests. L.D.M., R.M. and A.R contributed to the preparation of the samples. D.B., D.S. and D.G. supervised the project. All authors contributed to the discussion of the results and the text.

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Correspondence to Daniele Sanvitto or Dario Ballarini.

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Maggiolini, E., Polimeno, L., Todisco, F. et al. Strongly enhanced light–matter coupling of monolayer WS2 from a bound state in the continuum. Nat. Mater. (2023).

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