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TT: Fachverband Tiefe Temperaturen

TT 39: SC: Iron-Based Superconductors - 1111

TT 39.8: Vortrag

Freitag, 26. März 2010, 12:15–12:30, H19

Unusual disorder effects in La Fe As_1−δ O_0.9 F_0.1 as revealed by NMR spectroscopy — •Franziska Hammerath¹, Stefan-Ludwig Drechsler¹, Hans-Joachim Grafe¹, Guillaume Lang¹, Günter Fuchs¹, Günter Behr¹, Ilya Eremin², Maxim Korshunov^2,3, and Bernd Büchner¹ — ¹Leibniz-Institut für Festkörper- & Werkstoffforschung, Dresden, Germany — ²MPI für Physik komplexer Systeme, Dresden — ³L.V. Kirensky Inst. of Physics, Sib. Branch of Russ. Acad. Scs., Krasnoyarsk, Russia

We report ⁷⁵As NMR measurements of the spin-lattice relaxation in the superconducting state of LaFeAsO_0.9F_0.1 and As-deficient samples, LaFeAs_1−δO_0.9F_0.1 with a drastic change of the 1/T₁ temperature dependence below T_c from a T³-law for LaFeAsO_0.9F_0.1 to a T^β-law (β=5−6) for LaFeAs_1−δO_0.9F_0.1. T_c and the slope of the upper critical field near T_c increase unexpectedly in the As-deficient samples. Our results are discussed in terms of non-universal SC gaps in Fe-pnictides and the effect of As deficiency as an exotic case when nonmagnetic ’smart’ impurities even stabilize an s_±−wave superconductor as well as within a scenario of a disorder driven change to conventional s₊₊ superconductivity.

[1] H.-J. Grafe et al., Phys. Rev. Lett. 101, 047003 (2008).