Interlayer quantum coherence and anomalous stability of v=1 bilayer quantum Hall state

We have compared the stability of the v = 2, 1 and 2/3 quantum Hall states in a bilayer two-dimensional electron system by changing the total density and the density ratio of electrons in the two quantum wells. The following experimental results have been obtained: The v = 1 state is stable over a wide range of the density difference. It is least stable when the electron density is balanced. The state collapses when the total density is more than a critical value. The density ratio has a small influence on the stability of v = 1. These features are not shared by the other quantum Hall states. We argue that they give an indication of the interlayer quantum coherence. (C) 1998 Elsevier Science B.V. All rights reserved.