Dresden 2009 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 40: Superconductivity: Ferropnictides 1
TT 40.1: Talk
Thursday, March 26, 2009, 14:00–14:15, HSZ 03
Antiferromagnetic correlations in the normal state of LaFeAsO1−xFx with 0≤ x≤ 0.125 — •Rüdiger Klingeler, Norman Leps, Liran Wang, Christian Hess, Günter Behr, Vladislav Kataev, and Bernd Büchner — IFW Dresden, P.O. Box 270116, 01171 Dresden, Germany
We have studied the interplay of magnetism and superconductivity in LaFeAsO1−xFx with 0≤ x ≤ 0.125. For low doping with x≤ 0.04, our data confirm a moderate suppression of both the structural transition and the antiferromagnetic spin density wave formation. For x≥ 0.05, both anomalies are completely suppressed and superconductivity is observed. Remarkably, the temperature dependence of the normal state susceptibility well above TC is almost independent of doping, i.e. both the absolute value and the slope are nearly unchanged compared to the undoped case [1]. This implies at least local antiferromagnetic interactions which barely depend on hole doping although the ground state changes entirely from an orthorhombic antiferromagnetic poor metal (x≤ 0.04) to a tetragonal superconductor (x≥ 0.05). These surprising results are discussed in terms of (i) - pseudogap formation, (ii) - antiferromagnetic correlations, and (iii) - preformed bipolarons which might be relevant to the pairing mechanism.
[1] R. Klingeler et al., Preprint at http://arxiv.org/abs/0808.0708