Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 45: Superconductivity: Ferropnictides 2

TT 45.9: Talk

Friday, March 27, 2009, 12:30–12:45, HSZ 03

Electronic properties of iron pnictides in the normal state probed by NMR — •Franziska Hammerath¹, Guillaume Lang¹, Hans-Joachim Grafe¹, Dalibor Paar^1,2, Katarina Manthey¹, Nicholas Curro³, Günther Behr¹, Jochen Werner¹, and Bernd Büchner¹ — ¹IFW Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany — ²Dept. of Physics, Faculty of Science, Univ. of Zagreb, P. O. Box 331, HR-10002 Zagreb, Croatia — ³Dept. of Physics, Univ. of California, Davis, CA 95616, USA

We have performed ⁷⁵As, ¹³⁹La, and ⁵⁷Fe Nuclear Magnetic Resonance (NMR) measurements on the new LaO_1−xF_xFeAs superconductor. For x=0.1, NMR on all three nuclei shows that the local electronic susceptibility increases with increasing temperature in the normal state [1]. The scaling of all NMR shifts with respect to the macroscopic susceptibility indicates a single spin liquid. Relaxation measurements exhibit a similar temperature-dependence for (T₁T)⁻¹, and suggest that the dynamical susceptibility changes uniformly in q space with varying temperature. For x=0.05, in the underdoped regime, we find a Curie Weiss like increase of (T₁T)⁻¹ at low temperatures, indicating the onset of local moment fluctuations.

[1] H.-J. Grafe, G. Lang, F. Hammerath et al., arXiv:0811.4508, submitted to New Journal of Physics (invited paper, special issue on iron pnictides superconductors).