Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 53: Superconductivity: Fe-based Superconductors - 122

TT 53.8: Talk

Wednesday, April 2, 2014, 11:30–11:45, HSZ 201

Spin Fluctuations in doped Ba122 probed by NMR Spin Lattice Relaxation Rate — •Uwe Gräfe¹, Hannes Kühne^2,3, Saicharan Aswartham¹, Philip Kuhns², Arneil Reyes², Sabine Wurmehl^1,4, Bernd Büchner^1,4, and Hans-Joachim Grafe¹ — ¹IFW Dresden, Institute for Solid State Research, P.O. Box 270116, D-01171 Dresden, Germany — ²National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA — ³Helmholtz-Zentrum Dresden-Rossendorf, Dresden High Magnetic Field Laboratory, P.O. Box 510119, D-01314 Dresden, Germany — ⁴TU-Dresden, Institute for Solid State Physics, D-01062 Dresden, Germany

In this talk we take a closer look on Co doped Ba122 by the local probe technique of NMR. Like many other iron pnictides Co doped Ba122 shows an increased spin lattice relaxation rate (SLR) above the superconducting transition temperature which hints at enhanced antiferromagnetic spin fluctuations (SF). These fluctuations are debated to play a crucial role for the pairing mechanism of superconductivity (SC). However, evidence for progressive slowing of SF in F doped La1111 (PRB 88, 104503) as well as evidence for cluster spin glass behavior in underdoped Ba122 (PRL 111, 207201) points at a competition of SC and antiferromagnetic order. We investigated the field dependence of the SLR in optimally Co doped Ba122 in detail to gain insights into the nature of spin fluctuations and their relevance for SC.