“Excitoner”: Stimulated amplification and propagation of excitons' beams Á. R. Vasconcellos, M. V. Mesquita and R. Luzzi Europhys. Lett., 49 5 (2000) 637-643 Published online: 01 September 2002 DOI: 10.1209/epl/i2000-00198-7