MANY-BODY INTEGER QUANTUM HALL-EFFECT - EVIDENCE FOR NEW PHASE-TRANSITIONS

The nu = 1 quantum Hall effect in bilayer 2D electron systems is shown to continuously evolve from a regime dominated by single-particle tun neling into one where interlayer Coulomb interactions stabilize the st ate. This many-body integer quantum Hall state exhibits a phase transi tion to a compressible state at large layer separation. We also find e vidence for an intriguing and unexpected second transition to a new in compressible state, driven by an in-plane magnetic field. While the or igin of this last result is unclear, we discuss a recent model of a ps eudospin textural phase transition.