The role of density imbalance in the νT=1 exciton condensate state for electron bilayer systems

We report on our experimental work involving the nu(T) = I exciton condensate in independently contacted bilayer two-dimensional electron systems. A phase diagram between the weakly coupled (nu(U) = 1/2, nu(L) = 1/2) phase and the strongly coupled nu(T) = 1 phase is experimentally investigated as a function of d/l(B) and electron density imbalance Delta n (equivalent to [n(L) - nU]/n(T)) using a drag current configuration. For imbalanced electron layer densities, small interlayer imbalances lead to strengthening of the excitonic phase. Here density imbalance leads to a phase boundary in the drag layer which is symmetric around zero imbalance. Surprisingly this behavior is not seen for rho(drive,xx), where an unusual asymmetric behavior around zero im-balance occurs. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim