“Phase competition and soft-core vortices in the O(2)xO(2) nonlinear sigma model”

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• Dr Chris Hooley SUPA, University of St Andrews
• Thursday 20 February 2014, 13:45-15:00
• Theory Library.

If you have a question about this talk, please contact Kevin Ralley.

Phase competition at low temperatures and phase reconstruction near quantum critical points are two current themes in condensed matter physics. In this talk, I shall analyse a model that has recently been discovered to contain interesting versions of both: the d=2 O(2)xO(2) nonlinear sigma model.

I shall begin by discussing its ground-state phase diagram, which has recently been shown [1] to exhibit an interesting phase coexistence region with an O(4) high-symmetry point in the middle of it. I shall then proceed to discuss the finite-temperature phase diagram, and explain the results that my collaborators and I have established so far. The main one of these is the physical mechanism for the suppression of the Berezinskii-Kosterlitz-Thouless transition as the O(4) point is approached, viz. the ‘eating away’ of the cores of vortices by the competing phase [2]. Finally, I shall indicate some open questions that are raised by this work [3].

No prior knowledge of Berezinskii-Kosterlitz-Thouless or of nonlinear sigma models is assumed; indeed, a decent fraction of the talk is introductory material. All are welcome!

[1] A. Jaefari, S. Lal, and E. Fradkin, Phys. Rev. B 82 , 144531 (2010). [2] J.M. Fellows, S.T. Carr, CAH , and J. Schmalian, Phys. Rev. Lett. 109, 155703 (2012). [3] CAH , S.T. Carr, J.M. Fellows, and J. Schmalian, arXiv:1311.5344 (to appear in JPSJ ).

This talk is part of the Theoretical Physics Seminars series.

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