Spin-Excitation-Instability-Induced Quantum Phase Transitions in   Double-Layer Quantum Hall Systems
  We study intersubband spin density collective modes in double-layer quantum Hall systems at $\nu=2$ within the time-dependent Hartree-Fock approximation. We find that these intersubband spin density excitations 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 antiferromagnetic phase is energetically stable and that the phase transition is continuous. 
Lian Zheng, R.J. Radtke and S. Das Sarma (Univ. of Maryland)