Bose-Einstein condensation of excitons in two dimensions

Abstract

Bose-Einstein condensation (BEC) is shown to exist for a noninteracting system in two dimensions, provided that the single-particle energy levels have a discrete spectrum below the continuum of extended states. This BEC, unlike that for three-dimensional Bose gases, possesses off-diagonal order only of finite range, and is thus not in violation of the Hohenberg theorem. The observation of such a BEC in the transport properties of excitons moving on the heterointerface of a type-II semiconductor superlattice is suggested, bearing in mind the fact that the random potential fluctuations would give rise to localized states on such surfaces.