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Quantum impurity in an antiferromagnet: non-linear sigma model theory

Subir Sachdev·Matthias Vojta
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Abstract

We present a new formulation of the theory of an arbitrary quantum impurity in an antiferromagnet, using the O(3) non-linear sigma model. We obtain the low temperature expansion for the impurity spin susceptibilities of antiferromagnets with magnetic long-range order in the ground state. We also consider the bulk quantum phase transition in d=2 to the gapped paramagnet (d is the spatial dimension): the impurity is described solely by a topological Berry phase term which is an exactly marginal perturbation to the critical theory. The physical properties of the quantum impurity near criticality are obtained by an expansion in (d-1).

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Subir Sachdev, Matthias Vojta. 2003-03-04. Quantum impurity in an antiferromagnet: non-linear sigma model theory. https://doi.org/10.1103/physrevb.68.064419

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