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Bilayer quantum Hall excitons: evidence for a finite temperature phase transition


When the separation between two parallel 2D electron systems becomes comparable to the average distance between electrons within a single layer, the system can support a strongly correlated phase at total filling factor n T = 1. This phase exhibits a spontaneous interlayer phase coherence which may be described as an excitonic Bose condensate. We study the Joshepson-like interlayer tunneling signature of this state as a function of the effective separation between the two layers, the interlayer charge imbalance, and temperature. The interlayer tunneling amplitude dependence on the layer spacing at various temperatures obeys an empirical power law scaling, and the layer separation where the tunneling disappears scales linearly with temperature. Our results offer evidence [1] that a finite temperature phase transition, a first in a quantum Hall system, separates the interlayer excitonic phase from incoherent phases which lack strong interlayer correlations. The phase boundary is found to be re-entrant as a function of charge imbalance thus suggesting an intricate competition between the bilayer coherent phase and independent layer states.   [1] A.R. Champagne, J.P. Eisenstein, L.N. Pfeiffer, K.W. West, Phys. Rev. Lett. (in press) Cond-mat/0709.0718

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Dr. Alexandre Champagne  is a candidate for the Experimental Condensed Matter Physics Position.