Disorder Effects on Exciton–Polariton Condensates

The impact of a random disorder potential on the dynamical properties of Bose–Einstein condensates is a very wide research field. In microcavities, these studies are even more crucial than in the condensates of cold atoms, since random disorder is naturally present in the semiconductor structures. In this chapter, we consider a stable condensate, defined by a chemical potential, propagating in a random disorder potential, like a liquid flowing through a capillary. We analyze the interplay between the kinetic energy, the localization energy, and the interaction between particles in 1D and 2D polariton condensates. The finite lifetime of polaritons is taken into account as well. In the first part, we remind the results of [Malpuech et al., Phys. Rev. Lett. 98, 206402 (2007)] where we considered the case of a static condensate. In that case, the condensate forms either a glassy insulating phase at low polariton density (strong localization), or a superfluid phase above the percolation threshold. We also show the calculation of the first-order spatial coherence of the condensate versus the condensate density. In the second part, we consider the case of a propagating noninteracting condensate which is always localized because of Anderson localization. The localization length is calculated in the Born approximation. The impact of the finite polariton lifetime is taken into account as well. In the last section, we consider the case of a propagating interacting condensate where the three regimes of strong localization, Anderson localization, and superfluid behavior are accessible. The localization length is calculated versus the system parameters. The localization length is strongly modified with respect to the noninteracting case. It is infinite in the superfluid regime, whereas it is strongly reduced if the fluid flows with a supersonic velocity (Cerenkov regime).