Canted antiferromagnetic and spin singlet quantum Hall states in double-layer systems
Abstract
We study double-layer quantum Hall systems at a total filling nu=2*nu_1, where a single layer at filling nu_1 forms a spin-polarized incompressible quantum Hall state. For nu_1=1, a detailed Hartree-Fock analysis is carried out on a realistic, microscopic Hamiltonian. For general nu_1, closely related results are obtained by a continuum quantum field theory using a non-linear sigma model. We find two new quantum Hall phases: one with a finite interlayer in-plane antiferromagnetic spin ordering (the `canted' state), and the other a spin singlet. For vanishing Zeeman energy the canted antiferromagnetic phase continuously goes over to a Neel phase. The quantum transitions between the various quantum Hall states are continuous, and are signaled by the softening of collective intersubband spin density excitations. Because of the broken symmetry, the canted phase supports a linear Goldstone mode and has a finite temperature Kosterlitz-Thouless transition. We present detailed results on the form of the phase diagram, magnitude of the canted order parameter, the collective excitation dispersions, the specific heat, the form of the dynamic light scattering spectrum at finite temperature, and the Kosterlitz-Thouless critical temperature. In particular, the existence and the significance of quantum multicritical points in the phase diagram are discussed in some detail. Our findings are consistent with recent light scattering experimental results. Other possible measurements, including thermodynamic and transport studies, are pointed out.Keywords
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