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arXiv · 0912.3682

Unusual disorder effects in superconducting LaFeAs_(1-d)O_0.9F_0.1 as revealed by NMR spectroscopy

F. Hammerath·S. -L. Drechsler·H. -J. Grafe·G. Lang·G. Fuchs·G. Behr·I. Eremin·M. M. Korshunov·B. Buechner
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Abstract

We report 75As NMR measurements of the spin-lattice relaxation in the superconducting state of LaFeAsO_(0.9)F_(0.1) and As-deficient LaFeAs_(1-d)O_0.9F_0.1. The temperature behavior of 1/T_1 below T_c changes drastically from a T^3-dependence for LaFeAsO_(0.9)F_(0.1) to a T^5-dependence for the As-deficient sample. These results, together with the previously reported unexpected increase of T_c and the slope of the upper critical field near T_c for the As-deficient sample, are discussed in terms of non-universal SC gaps in Fe-pnictides and the effect of As deficiency as an exotic case where nonmagnetic 'smart' impurities even stabilize an s+- wave superconductor or within a scenario of a disorder-driven change to s++ superconductivity.

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F. Hammerath, S. -L. Drechsler, H. -J. Grafe, G. Lang, G. Fuchs, G. Behr, I. Eremin, M. M. Korshunov, B. Buechner. 2010-03-31. Unusual disorder effects in superconducting LaFeAs_(1-d)O_0.9F_0.1 as revealed by NMR spectroscopy. https://doi.org/10.1103/physrevb.81.140504

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