Macroscopically ordered state in an exciton system

• Published in: Nature (London) Vol. 418; no. 6899; pp. 751 - 754
• Main Authors: Butov, L. V, Gossard, A. C, Chemla, D. S
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 15.08.2002
• Subjects: Electrons; Emission measurements; Gases; Helium; Low temperature; Particle physics; Scientific imaging; Semiconductors
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature00943

There is a rich variety of quantum liquids-such as superconductors, liquid helium and atom Bose-Einstein condensates-that exhibit macroscopic coherence in the form of ordered arrays of vortices. Experimental observation of a macroscopically ordered electronic state in semiconductors has, however, remained a challenging and relatively unexplored problem. A promising approach for the realization of such a state is to use excitons, bound pairs of electrons and holes that can form in semiconductor systems. At low densities, excitons are Bose-particles, and at low temperatures, of the order of a few kelvin, excitons can form a quantum liquid-that is, a statistically degenerate Bose gas or even a Bose-Einstein condensate. Here we report photoluminescence measurements of a quasi-two-dimensional exciton gas in GaAs/AlGaAs coupled quantum wells and the observation of a macroscopically ordered exciton state. Our spatially resolved measurements reveal fragmentation of the ring-shaped emission pattern into circular structures that form periodic arrays over lengths up to 1 mm.