All-optical photonic time crystal in a surface-plasmon cavity metamaterial

Floquet driving of carriers in a surface-plasmon cavity metamaterial breaks the barrier to all-optical photonic time crystals, revealing emergent gain at terahertz frequencies.

Photonic time crystals (PTCs) have periodically modulated optical properties in the time domain. As temporal analogs of spatial photonic crystals, they have been eagerly sought for their unique momentum gaps (k-gaps), with the ability to sustain exponentially growing/decaying modes in time. Floquet driving was considered as a route to realize PTCs. However, previous experimental realizations have been confined to electrical circuits. Extending this concept beyond the microwave regime remains notoriously challenging, as it requires simultaneous near-unity modulation depth and sub-optical-cycle coherent driving. Now, Tingwen Guo and colleagues at Laboratoire des Solides Irradiés and other institutions reported one of the first all-optical realizations of a PTC at terahertz frequencies [1].

The authors use a surface-plasmon cavity metamaterial made of a metal–insulator–InSb (Au/Si₃N₄/InSb) structure, driven by a multi-cycle terahertz field at 0.69 THz. Owing to the non-parabolic conduction band, the effective mass of carriers in InSb can be modulated by as much as 80% of their rest mass, inducing near-unity modulation of the plasmonic resonance at twice the drive frequency. Frequency-resolved pump–probe spectroscopy was employed to track the driven system’s response. Floquet analysis was applied and the transition to the PTC regime was identified, where two Floquet eigenmodes coalesce and PT symmetry is spontaneously broken. Beyond this exceptional point, one mode exhibits reduced damping: a linewidth narrowing of approximately 40 GHz was observed, corresponding to a reduction in non-radiative plasmonic losses of over 50%. Based on the measured parameters, the authors further predict plasmonic lasing with optimized cavity designs.

This work establishes a robust platform for time-domain photonics in plasmonic systems, demonstrating that dissipation can be actively engineered through temporal modulation. The mechanism is scalable toward higher frequencies, opening new pathways for light amplification and ultrafast optical control.

References

[1] Guo , T. , Sueiro , J. , Andolina , G.M. , Levchuk , A. , Ponzoni , S. , Grasset , R. , Monthe , D. , Aupiais , I. , Daineka , D. , Briatico , J. , de Oliveira, T.V.A.G. , Ponomaryov , A. , Arshad , A. , Karimbana-Kandy , A. , Prajapati , G.L. , Ilyakov , I. , Deinert , J.C. , Maehrlein , S.F. , Perfetti , L. , Schirò , M. , Laplace , Y. : Plasmonic metamaterial time crystal. Nature 656(8127), 343–348(2026)

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