Metallic spin density wave in iron-based superconductors

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Date/Time:Wednesday, 10 Mar 2010 from 4:10 pm to 5:00 pm
Location:Physics 5
Channel:Condensed Matter Physics
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Prof. Ilya Eremin (Max-Planck-Institut für Physik komplexer Systeme, Dresden und Institut für Theoretische Physik, TU Braunschweig, Germany)

Recent discovery of superconductivity in the iron-based layered pnictides with Tc ranging between 26 and 56K generated enormous interest in the physics of these materials. The superconductivity has been discovered in oxygen containing RFeAsO (R=La, Nd, Sm) as well as in oxygen free AFe2As2 (A=Ba, Sr, Ca). Like the cuprates, the pnictides are quai-two-dimensional, their parent material shows antiferromagnetic long-range order below 2000K and superconductivity occurs upon doping of either electrons or holes into the FeAs layers.
In my talk I will analyze the selection of the stripe magnetic order in the unfolded BZ within itinerant description. Selecting one hole and two electron pockets we found that SDW order is highly degenerate if electron pockets are circular and interactions involved are between holes and electrons only. Repulsive charge interactions between two electrons as well as ellipticity of the electron pockets break the degeneracy and select metallic (0, π) [(π,0)] SDW state in the unfolded BZ -- the same order as seen in the experiments. We found that the SDW state remains a metal even for the case of a perfect nesting because one combination of the two hole operators and one combination of two electron operators decouple from the SDW mixing. We further discuss the resulting spin wave spectrum in the SDW state and the resulting quasiparticle interference patterns.