Superfluidity and Vortex Lattice Formation in Quasi Two-Dimensional Exciton System

Bose-Einstein condensation(BEC) and superfluidity of excitons in type-II quantum wells are studied theoretically. As a typical example, we consider GaAs/AlAs quantum wells with each layer thickness L less than 37Å. First, we investigate the interaction between excitons, thus finding it repulsive for L less than about 15Å, which shows the possibility of BEC. Secondly, we study the stationary pattern of the phase of the BEC order parameter under the external current J. The interaction between excitons and the weak laser light violates conservation of number of excitons and fixes that phase. There appears a vortex lattice with net supercurrent when J is larger than a critical value. The experimental observation of this critical current will give an evidence that BEC and superfluidity occur in exciton system.