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How to make a bilayer exciton condensate flow


Among the many examples of Bose condensation considered in physics, electron–hole-pair (exciton) condensation has maintained special interest because of controversy about condensate properties. Although ideal condensates can support an exciton supercurrent, it has not been clear how such a current could be induced or detected. This paper addresses the electrical generation of exciton supercurrents in bilayer condensates (systems in which the electrons and holes are in separate layers) and reaches a surprising conclusion. We find that steady-state dissipationless currents cannot be induced simply by connecting the two layers in series to guarantee opposite currents in electron and hole layers, as has long been supposed. Instead, current should be injected into and removed from the same layer, and a conducting channel supplied to close the counterflow portion of supercurrent in the other layer.

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Figure 1: Schematic illustration of a separately contacted bilayer exciton condensate.
Figure 2: Series-counterflow (S-CF) and drag-counterflow (D-CF) geometries.
Figure 3: One-dimensional toy-model self-consistent current distributions.


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This work has been supported by the Welch Foundation and by the National Science Foundation under grant DMR-0606489 and by SWAN-NRI. A.H.M. acknowledges long-standing interactions with J. Eisenstein, W. Dietsche and K. von Klitzing, which have informed this analysis, and discussions with M. Lilly, L. Tiemann and I. Spielman.

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Correspondence to Jung-Jung Su.

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Su, JJ., MacDonald, A. How to make a bilayer exciton condensate flow. Nature Phys 4, 799–802 (2008).

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