SPIN EFFECTS IN THE PHASE TRANSITION OF THE νT = 1 BILAYER ELECTRON SYSTEM

We present tilted-field experiments on a bilayer electron system at νT = 1 with negligible tunneling and demonstrate that the spin degree of freedom plays a decisive role in the ground-state phase diagram of the system. We observe that the phase boundary separating the incompressible quantum Hall state and a compressible state at d/ℓB = 1.90 (d: interlayer distance, ℓB: magnetic length) in a perpendicular field shifts to higher densities with tilt until it saturates at d/ℓB = 2.33. We develop a model describing the energies of the competing phases and show that the observed shift of the phase boundary reflects the spin-polarization dependence of the Coulomb and Zeeman energies of the compressible state. A new phase diagram as a function of d/ℓB and the Zeeman energy is established and its implications as to the nature of the phase transition are discussed.