Spin-Dependent Phase Diagram of the ν_T=1 Bilayer Electron System

We show that the spin degree of freedom plays a decisive role in the phase diagram of the ν_T=1 bilayer electron system using an in-plane field B_‖ in the regime of negligible tunneling. We observe that the phase boundary separating the quantum Hall and compressible states at d/ℓ_B=1.90 for B_‖=0 (d: interlayer distance, ℓ_B: magnetic length) steadily shifts with B_‖ before saturating at d/ℓ_B=2.33 when the compressible state becomes fully polarized. Using a simple model for the energies of the competing phases, we can quantitatively describe our results. A new phase diagram as a function of d/ℓ_B and the Zeeman energy is established and its implications as to the nature of the phase transition are discussed.