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Giant effective Zeeman splitting in a monolayer semiconductor realized by spin-selective strong light–matter coupling


Strong coupling between light and the fundamental excitations of a two-dimensional electron gas (2DEG) is of foundational importance both to pure physics and to the understanding and development of future photonic nanotechnologies1,2,3,4,5,6,7. Here we study the relationship between spin polarization of a 2DEG in a monolayer semiconductor, MoSe2, and light–matter interactions modified by a zero-dimensional optical microcavity. We find pronounced spin-susceptibility of the 2DEG to simultaneously enhance and suppress trion-polariton formation in opposite photon helicities. This leads to observation of a giant effective valley Zeeman splitting for trion-polaritons (g-factor of >20), exceeding the purely trionic splitting by over five times. Going further, we observe clear effective optical nonlinearity arising from the highly nonlinear behaviour of the valley-specific strong light–matter coupling regime, and allowing all-optical tuning of the polaritonic Zeeman splitting from 4 meV to >10 meV. Our experiments lay the groundwork for engineering topological phases with true unidirectionality in monolayer semiconductors, accompanied by giant effective photonic nonlinearities rooted in many-body exciton–electron correlations.

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Fig. 1: Excitations of a 2DEG strongly coupled to light in monolayer MoSe2.
Fig. 2: Giant effective trion-polariton Zeeman splitting.
Fig. 3: Trion-polariton effective nonlinearity.

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Data supporting the plots within this paper are available from the corresponding authors upon request.


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T.P.L. acknowledges financial support from the EPSRC Doctoral Prize Fellowship scheme (grant reference EP/R513313/1) and the JSPS Postdoctoral Fellowships for Research in Japan scheme. T.P.L., D.J.G., J.P., Y.O. and A.I.T. acknowledge support from the Royal Society International Exchange (grant no. IEC\R3\170088). T.P.L., D.J.G., A.G., C. Louca, L.K., I.A., M.B. and A.I.T. acknowledge support from an EPSRC Centre-to-Centre grant (no. EP/S030751/1). T.P.L., D.J.G. and A.I.T. additionally acknowledge financial support from the European Graphene Flagship Project (grant agreement no. 881603) and EPSRC (grants nos. EP/V006975/1, EP/P026850/1 and EP/V026496/1). C. Leblanc, D.S. and G.M. acknowledge support from projects EU ‘TOPOLIGHT’ (964770) and ‘QUANTOPOL’ (846353), from ANR Labex GaNEXT (ANR-11-LABX-0014) and the ANR programme ‘Investissements d’Avenir’ through the IDEX-ISITE initiative 16-IDEX-0001 (CAP 20-25). L.K., I.A. and M.B. acknowledge financial support from the Deutsche Forschungsgemeinschaft through the International Collaborative Research Centre 160 (project no. C2) and a UAR professorship, Mercur Foundation (grant no. Pe-2019-0022). We thank D. N. Krizhanovskii for useful discussions.

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T.P.L., D.J.G. and J.P. performed low-temperature magneto-optical spectroscopy. T.P.L., D.J.G., C. Leblanc, D.D.S., G.M. and A.I.T. analysed and discussed the bare flake and cavity spectroscopy data. C. Leblanc, D.D.S. and G.M. developed the cavity fitting model and rate equations. L.K. and I.A.A. collected and analysed time-resolved data. J.P. and P.M. deposited the EuS films onto DBR substrates. T.P.L., D.J.G., J.P. and P.M. performed SQUID magnetometry. C. Louca identified and transferred MoSe2 flakes onto EuS films. A.G. carried out electron density calculations. M.B., Y.O., G.M. and A.I.T. managed various aspects of the project. A.I.T. supervised the project. T.P.L. wrote the manuscript, with contributions from all co-authors.

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Correspondence to T. P. Lyons or A. I. Tartakovskii.

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

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Lyons, T.P., Gillard, D.J., Leblanc, C. et al. Giant effective Zeeman splitting in a monolayer semiconductor realized by spin-selective strong light–matter coupling. Nat. Photon. 16, 632–636 (2022).

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