Schedule Jun 08, 2004
Emergent Photons and New Transitions in the O(3)Sigma Model with Hedgehog Suppression
Olexei Motrunich (KITP)

We study the effect of hedgehog suppression in the O(3) sigma model in D=2+1. We show via Monte Carlo simulations that the sigma model can be disordered while effectively forbidding these point topological defects. The resulting paramagnetic state has gauge charged matter with half-integer spin (spinons) and also an emergent gauge field (photons), whose existence is explicitly demonstrated. The zero temperature ordering transition from this phase is found to be continuous but distinct from the regular Heisenberg ordering transition. We propose that these phases and this phase transition are captured by the noncompact CP1 model, which contains a pair of bosonic fields coupled to a noncompact U(1) gauge field. Direct simulation of the transition in this model yields critical exponents that support this claim. We also consider the easy-plane deformation of the model and the effects of a Zeeman field and finite temperature. Generalization to higher dimensions and the effects of nonzero hedgehog fugacity are discussed.

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