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 Karl Franzens University Graz

Graz University of Technology 

Monitoring adsorbate phases: A means to detect hidden order parameters
Prof. Dr. Erminald BERTEL
Institute of Physical Chemistry, University of Innsbruck, Austria
17:00 - 18:00 Tuesday 10 May 2011 KFU

A brief introduction will be given into the definition of order parameters and the Landau theory of phase transitions. The relevance of hidden order parameters in correlated and low-dimensional systems will be discussed. A quasi-one-dimensional adsorbate system on a strongly anisotropic metal surface, i.e. Br/Pt(110), is introduced and an anomalous phase transition is reported. The phase transition is rationalized by extending the Landau theory to include inter-adsorbate and adsorbate-substrate interactions. The model is then applied to the recently discovered iron-pnictide superconductors. While there is general agreement that the unconventional superconductivity in these compounds is somehow related to hidden order parameters, their nature is still being disputed. Application of the present ideas suggests an imminent charge-ordering instability in at least some members of this family.