Schedule
Quantum Hall Ferromagnets and Antiferromagnets
Subir Sachdev, Yale University
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 $\nu = 2$.
cond-mat/9807393, cond-mat/9709315
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