Letter

Room-temperature Bose–Einstein condensation of cavity exciton–polaritons in a polymer

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Abstract

A Bose–Einstein condensate (BEC) is a state of matter in which extensive collective coherence leads to intriguing macroscopic quantum phenomena1. In crystalline semiconductor microcavities, bosonic quasiparticles, known as exciton–polaritons, can be created through strong coupling between bound electron–hole pairs and the photon field2. Recently, a non-equilibrium BEC (ref. 3) and superfluidity4,5 have been demonstrated in such structures. With organic crystals grown inside dielectric microcavities, signatures of polariton lasing have been observed6. However, owing to the deleterious effects of disorder and material imperfection on the condensed phase7,8,9, only crystalline materials of the highest quality have been used until now. Here we demonstrate non-equilibrium BEC of exciton–polaritons in a polymer-filled microcavity at room temperature. We observe thermalization of polaritons and, above a critical excitation density, clear evidence of condensation at zero in-plane momentum, namely nonlinear behaviour, blueshifted emission and long-range coherence. The key signatures distinguishing the behaviour from conventional photon lasing are presented. As no crystal growth is involved, our approach radically reduces the complexity of experiments to investigate BEC physics and paves the way for a new generation of opto-electronic devices, taking advantage of the processability and flexibility of polymers.

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Acknowledgements

We acknowledge M. Sousa for help with the ellipsometry. We are grateful to B. J. Offrein, P. F. Seidler and G. La Rocca for insightful discussions, and to G. Rainò and F. Ding for assistance with the experiment. L.M. acknowledges financial support from the European project ‘ICARUS’ (IST-FP7-237900).

Author information

Author notes

    • Johannes D. Plumhof

    Present address: u2t photonics AG, Reuchlinstrasse 10/11, Berlin 10553, Germany

Affiliations

  1. IBM Research–Zurich, Säumerstrasse 4, Rüschlikon 8803, Switzerland

    • Johannes D. Plumhof
    • , Thilo Stöferle
    • , Lijian Mai
    •  & Rainer F. Mahrt
  2. Macromolecular Chemistry Group and Institute for Polymer Technology, Bergische Universität Wuppertal, Gauss-Strasse 20, 42119 Wuppertal, Germany

    • Ullrich Scherf

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Contributions

L.M. fabricated the samples. U.S. synthesized the polymer. J.D.P., T.S. and R.F.M. built the experimental set up and performed the measurements. T.S. wrote the manuscript with inputs from all other authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Thilo Stöferle.

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