Hydrodynamic transport of excitons in semiconductors and Bose-Einstein condensation

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Abstract
We study the expansion of an exciton gas against lattice drag, describe the transition between the diffusive and low-drag hydrodynamic regimes, and compare with experimental data obtained at exciton densities and temperatures near the Bose-Einstein phase boundary. As we show through numerical simulation, the rapid expansion of the exciton cloud seen experimentally at high exciton densities can be explained as drag-free hydrodynamic flow. Such a reduction in drag strongly suggests that Bose-Einstein condensation has occurred and that excitonic superfluidity is being observed.