Moiré pattern of interference dislocations and superfluidity in condensate of indirect excitons*

Interference patterns provide direct measurement of coherent propagation of matter waves in quantum systems. Dislocations in interference patterns is a basic phenomenon, which is observed in a variety of quantum systems including atoms, polaritons, magnons, and optical systems. Interference dislocations have been associated with vortices. In this work, we present a new mechanism – the moiré effect, which leads to the appearance of dislocations in interference patterns. We show that this mechanism is the origin of interference dislocations in condensate of indirect excitons (IXs). These interference dislocations are formed by IX condensate matter waves ballistically propagating over macroscopic distances. The long-range ballistic IX propagation is the evidence for IX condensate superfluidity. Superfluidity was predicted for IXs decades ago. The finding of IX condensate superfluidity in interference experiments is consistent with this theoretical prediction.