Edge excitations and the fractional quantum Hall effect in double quantum wells

The structure of the edge excitations of a quantum Hall droplet, confined in a double quantum well, is studied using a generalized version of the Wen-Stone chiral boson action. As the interwell tunneling, t, is increased, one finds a ``metal-insulator'' transition from a phase where the optic edge mode is ungapped to a phase where the optic mode is gapped. The large-t phase exhibits edge quasiexcitons whose charge is half that of a quasiparticle-quasihole bound state. The critical behavior of the conductances, the exciton gap, and the excitonic order parameter is discussed.