Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 20: Symposium Bose-Einstein Kondensation in Halbleitern
HL 20.4: Hauptvortrag
Dienstag, 27. März 2007, 12:15–12:45, H15
Signatures of excitonic condensates in quantum Hall bilayers — •Lars Tiemann1, Rodney Wiersma1, Sjoerd Lok1, Werner Dietsche1, Klaus v. Klitzing1, and Koji Muraki2 — 1Max-Planck Institute für Festkörperforschung, Heisenbergstr. 1, 70569 Stuttgart — 2NTT Basic Research Laboratories, Atsugi, Japan
Experiments on two closely spaced 2D electron double layers under strong perpendicular magnetic fields, where each layer’s filling factor is near 1/2, show signatures of a Bose-Einstein condensate of interlayer excitons. In drag experiments, where a current is flowing in only one layer, a quantized Hall voltage of h/e2 over both layers is observed while the longitudinal voltages vanish. This behavior is regarded as a consequence of interlayer lectron-hole pairs (=excitons) residing in the same quantum mechanical state, analogue to atomic Bose-Einstein condensates. Complementary experiments with counter flowing currents in both layers imply a superfluid-like transport mode of these interlayer excitons. While all previous work focused on Hall bars, our recent experiments performed on a ring structure reveal that the radial (or σxx) conductance in the current-carrying layer only slowly diminishes with decreasing temperature and a given coupling strength. In contrast to Hall bars, voltages of equal value build up over both layers even in the weak coupling limit and at temperatures exceeding 0.3 K. In the limit of T —→ 0 K and sufficiently strong coupling between the two layers, the conductance vanishes altogether and the voltages over both layers equal the externally applied excitation voltage.