High-T(c) ferroelectricity emerging from magnetic degeneracy in cupric oxide.

@article{Giovannetti2011HighTcFE,
  title={High-T(c) ferroelectricity emerging from magnetic degeneracy in cupric oxide.},
  author={Gianluca Giovannetti and Sanjeev Kumar and Alessandro Stroppa and Jeroen van den Brink and Silvia Picozzi and Jos{\'e} Lorenzana},
  journal={Physical review letters},
  year={2011},
  volume={106 2},
  pages={
          026401
        }
}
Cupric oxide is multiferroic at unusually high temperatures. From density functional calculations we find that the low-T magnetic phase is paraelectric, and the higher-T one is ferroelectric with a size and direction of polarization in good agreement with experiments. By mapping the ab initio results on to an effective spin model, we show that the system has a manifold of almost degenerate ground states. In the high-T magnetic state noncollinearity and inversion symmetry breaking stabilize each… 

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