Abstract

Polaritons with hyperbolic dispersion are key to many emerging photonic technologies, including subdiffraction imaging, sensing and spontaneous emission engineering1,2,3,4,5,6,7,8. Fundamental to their effective application are the lifetimes of the polaritons, as well as their phase and group velocities7,9. Here, we combine time-domain interferometry10 and scattering-type near-field microscopy11 to visualize the propagation of hyperbolic polaritons in space and time, allowing the first direct measurement of all these quantities. In particular, we study infrared phonon polaritons in a thin hexagonal boron nitride8,12,13 waveguide exhibiting hyperbolic dispersion and deep subwavelength-scale field confinement. Our results reveal—in a natural material—negative phase velocity paired with a remarkably slow group velocity of 0.002c and lifetimes in the picosecond range. While these findings show the polariton's potential for mediating strong light–matter interactions and negative refraction, our imaging technique paves the way to explicit nanoimaging of polariton propagation characteristics in other two-dimensional materials, metamaterials and waveguides.

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Acknowledgements

The authors thank F. Keilmann (University of Munich) and R. Huber (University of Regensburg) for discussions. The authors acknowledge support from the European Union through ERC starting grants (TERATOMO grant no. 258461 and SPINTROS grant no. 257654), the European Commission under the Graphene Flagship (contract no. CNECT-ICT-604391), the Spanish Ministry of Economy and Competitiveness (national projects MAT2012-36580 and MAT2012-37638) and the Basque Government (project PI2011-1). F.K. acknowledges support from the Fundacio Cellex Barcelona, ERC Career integration grant 294056 (GRANOP), ERC starting grant 307806 (CarbonLight) and project GRASP (FP7-ICT-2013-613024-GRASP).

Author information

Affiliations

  1. CIC NanoGUNE, E-20018, Donostia, San Sebastian, Spain

    • Edward Yoxall
    • , Martin Schnell
    • , Alexey Y. Nikitin
    • , Oihana Txoperena
    • , Félix Casanova
    •  & Luis E. Hueso
  2. IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain

    • Alexey Y. Nikitin
    • , Félix Casanova
    • , Luis E. Hueso
    •  & Rainer Hillenbrand
  3. ICFO – Institut de Ciències Fotòniques, Mediterranean Technology Park, E-08860 Castelldefels (Barcelona), Spain

    • Achim Woessner
    • , Mark B. Lundeberg
    •  & Frank H. L. Koppens
  4. CIC NanoGUNE and EHU/UPV, E-20018, Donostia, San Sebastian, Spain

    • Rainer Hillenbrand

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Contributions

E.Y., M.S. and R.H. conceived the study. E.Y. and M.S. performed the experiments. E.Y., M.S. and R.H. analysed the data and discussed the results. O.T. fabricated the sample. M.S., A.W., M.B.L. and A.Y.N. carried out simulations. E.Y., M.S. and R.H. wrote the manuscript. F.C., L.E.H., F.H.L.K. and R.H. supervised the work and discussed the manuscript. All authors contributed to the scientific discussion and manuscript revisions.

Competing interests

R.H. is co-founder of Neaspec GmbH, a company producing scattering-type scanning near-field optical microscope systems such as the one used in this study. All other authors declare no competing financial interests.

Corresponding author

Correspondence to Rainer Hillenbrand.

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DOI

https://doi.org/10.1038/nphoton.2015.166

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