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Macroscopically ordered state in an exciton system


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 vortices1,2,3,4. 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-particles5, 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 condensate5,6,7. 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.

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Figure 1: Radial dependence of the indirect exciton photoluminescence (PL).
Figure 2: Excitation density dependence of the spatial pattern of the indirect exciton PL intensity.
Figure 3: Temperature dependence of the spatial pattern of the indirect exciton PL intensity.
Figure 4: Schematics demonstrating a reduction of emission intensity for excitons in motion.


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We thank A.L. Ivanov for discussions, C.W. Lai and A.V. Mintsev for help in preparing the experiment and K.L. Campman for growing the high quality CQW samples. This work was supported by the Office of Basic Energy Sciences US Department of Energy and by the Russian Foundation for Basic Research (RFBR).

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Butov, L., Gossard, A. & Chemla, D. Macroscopically ordered state in an exciton system. Nature 418, 751–754 (2002).

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