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

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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Figure 1: Microcavity sample and dispersion relation.
Figure 2: Temperature-dependent thermalization of polaritons.
Figure 3: Emergence of room-temperature polariton BEC.
Figure 4: Spatial and temporal coherence.

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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).

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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.

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Correspondence to Thilo Stöferle.

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The authors declare no competing financial interests.

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Plumhof, J., Stöferle, T., Mai, L. et al. Room-temperature Bose–Einstein condensation of cavity exciton–polaritons in a polymer. Nature Mater 13, 247–252 (2014). https://doi.org/10.1038/nmat3825

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