SPIN-EXCITATION-INSTABILITY-INDUCED QUANTUM PHASE-TRANSITIONS IN DOUBLE-LAYER QUANTUM HALL SYSTEMS

We study intersubband spin density collective modes in double-layer qu antum Hall systems at upsilon = 2 within the time-dependent Hartree-Fo ck approximation. We find that these intersubband spin density excitat ions may soften under experimentally accessible conditions, signaling a phase transition to a new quantum Hall state with interlayer inplane antiferromagnetic spin correlations. We show that this novel canted a ntiferromagnetic phase is energetically stable and that the phase tran sition is continuous.