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IAP_Seminar am 18.12.2012

27 Nov 2012 by in VorträgeNeu

Alle interessierten Kolleginnen und Kollegen sind zu diesem Seminar
(45 min mit anschließender gemeinsamer Diskussion) herzlich eingeladen.


Termin: Dienstag, 18.12.2012 um 16:00 Uhr
Ort: Technische Universität Wien,
Institut für Angewandte Physik,
Seminarraum 134A, Turm B (gelbe Leitfarbe), 5. OG
1040 Wien, Wiedner Hauptstraße 8-10

Vortragender: Prof. Erminald Bertel
Institute of Physical Chemistry, University of Innsbruck

Thema: Surface Phases on 122 Fe Based Superconductors:
An Indication of Charge Density Wave Fluctuations?
In addition to the cuprate superconductors a second class of unconventional superconductors was
discovered in 2006 by Hideo Hasono, the iron-based superconductors. The discovery refueled the quest
for a rigorous theory of high-temperature superconductivity. Since in both classes of materials the parent
compounds exhibit antiferromagnetic order, which is quenched upon doping, it is widely assumed that
antiferromagnetic fluctuations are responsible for the pairing interaction. Recently, scanning tunneling
microscopy studies of the cleavage surfaces of so-called 122 Fe based superconductors revealed longrange
ordered structures with an unexpected temperature dependence. The observations sparked a
controversy about the origin of these surface phases.
We have found a similar anomalous phase transition in a much simpler system, i.e. halogens on the
strongly anisotropic Pt(110) surface. Here the phase transition is driven by charge density wave
fluctuations in the substrate. An extended Landau model of the phase transition is presented. The model
captures both, the temperature dependence and the relative stability of the different structures with
respect to chemical composition for halogen/Pt(110) as well as for the 122 Fe superconductors. The
proposed interpretation for the superconductor surface structures implies the presence of charge density
wave fluctuations with a wave vector differing from that of the antiferromagnetic spin fluctuations. If
confirmed, this model would offer an alternative channel for the pairing interaction.


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