Indirect excitons and dipolaritons
A spatially indirect exciton is a bound state of an electron and a hole localized in coupled parallel 2D layers. Electron and a hole wave functions show a very small overlap and consequently indirect excitons have a long lifetime as compare to ordinary excitons. They behave as metastable particles which allows their cooling beyond the temperature of a quantum degeneracy. The indirect excitons have been widely studied both experimentally and theoretically in recent years. Superfluid behavior of a system of indirect excitons was predicted by Lozovik and Yudson more 30 years ago and subsequent theoretical and experimental studies have suggested that this should be manifested in a series of remarkable effects, including persistent currents, Josephson-related phenomena and sponteneous pattern formation in the real space.