Some recent results on the interaction between two order parameters : the case of linear-quadratic coupling

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• Ekhard Salje (Department of Earth Sciences)
• Monday 07 November 2011, 16:15-17:00
• Harker 2 lecture room, Department of Earth Sciences, Downing Site.

If you have a question about this talk, please contact Ian Farnan.

The coupling between order parameters in systems with several instabilities has been analyzed within Landau theory. The dominant term considered in this paper is linear in one order parameter and quadratic in the second order parameter ~ QP2 , other coupling terms have been treated previously. Typical examples for Q are proper or pseudo-proper ferroelastic instabilities, while P might be octahedral tilting in a perovskite, (anti-) ferromagnetic ordering or (anti) ferroelectric soft modes. Coupling of this type is common in fluorites, Verwey transitions, Jahn Teller systems, pnictide super conductors etc. Analytical solutions and characteristic phase diagrams of the stable configurations are compiled. The coupling can lead to stepwise phase transitions even when the uncoupled systems would show continuous transitions. Mixed phase are common, so that many ‘intermediate phases’ described in literature are in fact the result of this linear-quadratic coupling.

This talk is part of the Mineral Sciences Seminars series.

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• Department of Earth Sciences seminars
• Harker 2 lecture room, Department of Earth Sciences, Downing Site
• Mineral Sciences Seminars

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