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Advances in Condensed Matter Physics
Volume 2011, Article ID 349362, 10 pages
Review Article

Coherence and Disorder in Bilayer Quantum Hall Systems

1Department of Physics, Indiana University, Bloomington, IN 47405, USA
2Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA

Received 25 May 2010; Accepted 1 October 2010

Academic Editor: Melinda Kellogg

Copyright © 2011 H. A. Fertig and Ganpathy Murthy. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The quantum Hall bilayer at total filling factor 𝑣 = 1 displays a number of properties akin to superfluidity, most clearly apparent in its very low dissipation in tunneling and counterflow transport. Theoretical descriptions in terms of quantum Hall ferromagnetism or thin-film superfluidity can be developed to explain these phenomena. In either case, merons can be identified as important low energy excitations. We demonstrate that a model in which puddles of merons induced by disorder, separated by narrow regions of interlayer coherence—a coherence network—can naturally explain many of the imperfect superfluid finite temperature properties that are observed in these systems. The periodic realization of this model shows that there can be low energy excitations beyond the superfluid mode. These are associated with transitions between states of different meron number in the puddles, where we argue that merons should be unbound at any temperature, and which can have important implications for the effect of quantum fluctuations on the system.