Schedule
Quantum Hall Ferromagnets and Antiferromagnets
Subir Sachdev, Yale University
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Single and double layer quantum Hall systems constitute some of the
most attractive experimental systems to study quantum phases and
phase transitions of spin systems. I begin by reviewing the low
temperature magnetic properties of a single quantum Hall layer
at a filling fraction $\nu = 1/m$ (where $m$ is an odd integer)
which realizes a two-dimensional quantum ferromagnet with a quantized
ground state magnetic moment. Then I consider double layer systems
at $\nu = 2/m$, when two such layers are brought in the vicinity of each
other. The new physics is now the antiferromagnetic
superexchange interaction between the layers, and this leads to a number
of interesting new quantum phases. Some univeral properties of the
quantum phase transitions are obtained by quantum Monte Carlo simulations
on model lattice spin systems. I close the talk with a survey of
recent experiments on double layer quantum Hall systems at $\nu = 2$.
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cond-mat/9807393, cond-mat/9709315
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