Résumé:

A mechanism for exciton Bose condensation is suggested. We show that the interaction of localized exciton magnetic polarons (EMP's) can lead to the formation of a free collective exciton magnetic polaron (CEMP) able to move as a whole particle. Critical conditions for this transition and characteristics of the CEMP are found. We interpret the recent data on giant magnetic polaron mobility in ZnSe/ZnMnxSe1-x quantum wells [G. A. Balchin, C. D. Poweleit, and L. M. Smith, in Proceedings of the 23rd International Conference on the Physics of Semiconductors, edited by M. Scheffler and R. Zimmermann (World Scientific, Singapore 1996), p. 2055] as a manifestation of the free CEMP formation due to clusterization of long-living indirect EMP's. [S0163-1829(98)52308-9].