Quantized Vortices and Four-Component Superfluidity of Semiconductor Excitons.

We study spatially indirect excitons of GaAs quantum wells, confined in a 10 mu m electrostatic trap. Below a critical temperature of about 1 K, we detect macroscopic spatial coherence and quantized vortices in the weak photoluminescence emitted from the trap. These quantum signatures are restricted to a narrow range of density, in a dilute regime. They manifest the formation of a four-component superfluid, made by a low population of optically bright excitons coherently coupled to a dominant fraction of optically dark excitons.