Luminescence patterns in photoexcited quantum wells: diffusion of the Coulomb plasma versus exciton superfluidity

Inspired by experimental observations of ring-like luminescence patterns outside the laser spot in double and single quantum wells (QWs), we performed molecular dynamics (MD) simulations of the electron-hole plasma. Electron and hole density profiles generally follow the hydrodynamic two-fluid kinetic equations with non-trivial power laws for hole and electron velocities. While the MD or its kinetic approximation explain the inner ring formation, they fail to account for the macroscopic outer luminesce rings observed both in double and single QWs. Solving the Gross-Pitaevskii equation we show that in contrast to previous theoretical models describing the outer ring formation via conventional (normal state) diffusion, this phenomenon is a sequence of superfluidity of excitons in a dark state.