We discuss models of the modulational instability in a cold exciton system incoupled quantum wells. One mechanism involves exciton formation in aphotoexcited electron-hole system in the presence of stimulated bindingprocesses which build up near exciton degeneracy. It is shown that suchprocesses may give rise to Turing instability leading to a spatially modulatedstate. The structure and symmetry of resulting patterns depend ondimensionality and symmetry. In the spatially uniform 2d electron-hole system,the instability leads to a triangular lattice pattern while, at anelectron-hole interface, a periodic 1d pattern develops. Wavelength selectionmechanism is analyzed, revealing that the transition is abrupt (type I) for theuniform 2d system, and continuous (type II) for the electron-hole interface.Another mechanism that could possibly drive the instability involves long-rangeattraction of the excitons. We illustrate how such an interaction can resultfrom current induced by exciton recombination ('plasmon wind'), derivestability criterion, and discuss likelihood of such a scenario.
展开▼
