ABSTRACT
Among the broken symmetry states that occur in many-particle systems, those in which long range phase coherence is established, either for bosons [1] or for pairs of fermions [2 ], have a special significance because of the quantum nature of their macroscopic order and the sometimes startling phenomenology that results. In semiconductors, the possibility of longrange phase coherence due to Bose condensation of excitons was first raised [3] nearly 40 years ago. In this paper, we argue that the anomalous transport properties discovered in bilayer quantum Hall systems by J. P. Eisenstein and collaborators [4], and studied in this group over the past couple of years, are an experimental manifestation of such an ordered state. We also briefly discuss the microscopic physics that causes this order to occur in the quantum Hall regime and efforts, currently in progress, to achieve a more complete understanding [5] of the collective transport effects that lie behind the experimental observations. This paper focuses on work related to these questions performed at the University of Texas.
