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Thursday, May 7th 2015

1:15 pm:

Despite having finite spin correlation lengths at nonzero temperatures, frustrated two-dimensional Heisenberg magnets can develop long-range discrete order driven by short-range thermal spin fluctuations. Indeed this "order from disorder" phenomenon can lead to a finite-temperature Ising or Potts transition; it has recently been realized experimentally in the iron-based superconductors where it is responsible for the high-temperature nematic phase. We can also ask whether such a mechanism can lead to an emergent critical phase in an isotropic Heisenbergm magnet and we present a model where this is indeed the case. Our results are supported by both Wilson-Polyakov scaling and by Friedan's geometrical approach to nonlinear sigma models. We also discuss recent computational studies that support our results and discuss possible experimental realizations. We end with a more general discussion of the relation between Friedan scaling and 2D antiferromagnetism, and the possibility of using it to simulate generalized surgery-free Ricci flows of topological manifolds of broader mathematical interest.

Work done in collaboration with P. Orth, R. Fernandes, B. Jeevanesan, J. Schmalian, P. Coleman and A.I. Larkin.

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