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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