Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: SC: Iron-Based Superconductors - 122

TT 34.10: Talk

Thursday, March 25, 2010, 16:30–16:45, H20

Magnetic fluctuations and superconductivity in Fe pnictides probed by Electron Spin Resonance — •Nikola Pascher¹, Joachim Deisenhofer¹, Hans-Albrecht Krug von Nidda¹, H. S. Jeevan², P. Gegenwart², and Alois Loidl¹ — ¹Experimentalphysik V, Center for Electronic Correlations and Magnetism, Institute for Physics, Augsburg University, D-86135 Augsburg, Germany — ²I. Physik. Institut, Georg-August-Universitaet Goettingen, D-37077 Goettingen, Germany

The electron spin resonance absorption spectrum of Eu²⁺ ions serves as a probe of the normal and superconducting state in Eu_0.5K_0.5Fe₂As₂. The spin-lattice relaxation rate 1/T₁^ESR obtained from the ESR linewidth exhibits a Korringa-like linear increase with temperature above T_C evidencing a normal Fermi-liquid behavior. Below 45 K deviations from the Korringa-law occur which are ascribed to enhanced magnetic fluctuations upon approaching the superconducting transition. Below T_C the spin lattice relaxation rate 1/T₁^ESR follows a T^1.5-behavior without the appearance of a coherence peak.