Nature457, 291-295 (15 January 2009) | doi:10.1038/nature07640; Received 26 August 2008; Accepted 13 November 2008
Collective fluid dynamics of a polariton condensate in a semiconductor microcavity
A. Amo1, D. Sanvitto1, F. P. Laussy2, D. Ballarini1, E. del Valle2, M. D. Martin1, A. Lemaître3, J. Bloch3, D. N. Krizhanovskii4, M. S. Skolnick4, C. Tejedor2 & L. Viña1
Departamento Física de Materiales,
Departamento Física Teórica de la Materia Condensada, Universidad Autonóma de Madrid, 28049 Madrid, Spain
LPN/CNRS, Route de Nozay, 91460 Marcoussis, France
Department of Physics & Astronomy, University of Sheffield, Sheffield S3 7RH, UK
Correspondence to: D. Sanvitto1 Correspondence and requests for materials should be addressed to D.S. (Email: daniele.sanvitto@uam.es).
Semiconductor microcavities offer unique systems in which to investigate the physics of weakly interacting bosons. Their elementary excitations, polaritons—mixtures of excitons and photons—can accumulate in macroscopically degenerate states to form various types of condensate in a wide range of experimental configurations, under either incoherent1, 2 or coherent3, 4 excitation. Condensates of polaritons have been put forward as candidates for superfluidity5, 6, and the formation of vortices7 as well as elementary excitations with linear dispersion8 are actively sought as evidence to support this. Here, using a coherent excitation triggered by a short optical pulse, we have created and set in motion a macroscopically degenerate state of polaritons that can be made to collide with a variety of defects present in the microcavity. Our experiments show striking manifestations of a coherent light–matter packet, travelling at high speed (of the order of one per cent of the speed of light) and displaying collective dynamics consistent with superfluidity, although one of a highly unusual character as it involves an out-of-equilibrium dissipative system. Our main results are the observation of a linear polariton dispersion accompanied by diffusionless motion; flow without resistance when crossing an obstacle; suppression of Rayleigh scattering; and splitting into two fluids when the size of the obstacle is comparable to the size of the wave packet. This work opens the way to the investigation of new phenomenology of out-of-equilibrium condensates.
