  Emergence of algebraic quasi-long-range order is a key feature of superfluid
phase transitions at two dimensions. For this reduced dimensionality
interactions prevent Bose-Einstein condensation with true long range order, at
any finite temperature. Here, we report the occurence of algebraic order in a
strongly interacting quantum liquid formed by dipolar excitons confined in a
bilayer semiconductor heterostructure. We observe a transition from exponential
to algebraic decay of the excitons temporal coherence, accompanied by a
universal scaling behaviour of the equation of state. Our results provide
strong evidence for a Berezinskii-Kosterlitz-Thouless (BKT) transition in a
multi-component boson-like system governed by strong dipolar interactions.

Quantum Gases