Abstract
New results point to surprising differences between fluids of light created in two-dimensional semiconductors and quantum fluids of matter particles. Unless a system is strongly anisotropic, the fluid of light cannot establish a single giant wave as conventional particles do in a Bose-Einstein condensate.
Highlights
One of the most striking discoveries to emerge from the study of nonequilibrium systems is that they sometimes exhibit ordered states that are impossible in their equilibrium counterparts
It has been shown [1] that a two-dimensional “flock”—that is, a collection of moving, self-propelled entities—can develop long-ranged orientational order in the presence of finite noise and in the absence of both rotational symmetry-breaking fields and longranged interactions
We report an example of the opposite phenomenon: a driven, two-dimensional Bose system, such as a gas of polariton excitations in a two-dimensional isotropic quantum well [3], cannot exhibit off-diagonal algebraic correlations [4]
Summary
One of the most striking discoveries to emerge from the study of nonequilibrium systems is that they sometimes exhibit ordered states that are impossible in their equilibrium counterparts. It is crucial to have both dissipation and driving, giving rise to a true nonequilibrium steady-state situation This conclusion follows from the known [11,12,13,14] connection between the complex Ginzburg-Landau equation (which describes the long-wavelength dynamics of a driven condensate) and the Kardar-Parisi-Zhang (KPZ) equation [15] or, in the anisotropic case, the anisotropic KPZ equation [16], which were originally formulated to describe randomly growing interfaces. In a driven system, the relation Hd 1⁄4 RHc is not satisfied, in general, because the dissipative and coherent parts of the dynamics are generated by independent processes This relation can, arise as an emergent symmetry at low frequencies and long wavelengths, as was shown to be the case for a three-dimensional driven condensate [9,10]. We shall derive the hydrodynamic long-wavelength description of a two-dimensional driven condensate and determine if it flows to effective thermal equilibrium
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