Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 45: Superconductivity: Ferropnictides 2
TT 45.7: Vortrag
Freitag, 27. März 2009, 12:00–12:15, HSZ 03
Orbital and spin effects for the upper critical field in strongly disordered iron pnictide superconductors — •Guenter Fuchs1, Stefan-Ludwig Drechsler1, Nadezhda Kozlova1, Konstantin Nenkov1, Guenter Behr1, Ernest Arushanov1,2, Jens Freudenberger1, Ruediger Klingeler1, Anke Koehler1, Bernd Buechner1, and Ludwig Schultz1 — 1IFW-Dresden, P.O. Box 270116, D-01171 Dresden, Germany — 2Inst. of Appl. Phys., Acad. Sci. Moldova, Chisinau, Moldova
We report upper critical field Bc2(T) [1], resistivity, and Hall data for disordered (arsenic deficient) LaO0.9F0.1FeAs1−δ in a wide temperature and field range up to 47 T. Due to the large linear initial slope of Bc2≈ -5.4 to -6.6T/K near Tc≈ 28.5 K the T-dependence of the in-plane Bc2(T) shows a clear flattening already near 23 K above 30 T which is intepreted as the onset of a Pauli-limited behavior with Bc2(0)≈ 63 to 68 T. Our results are discussed in terms of disorder effects within scenarios for conventional and unconventional superconductivity (SC). Proposed unconventional p- and d-wave scenarios of SC can be discarded for our samples. The enhancement of the upper critical field slope near Tc by strong disorder provides evidence for an important attractive intraband contribution to the pairing of Cooper pairs in the Fe pnictides. We compare our results with Bc2-data in the literature which show often no Pauli-limiting behavior. A novel disorder related scenario of a complex interplay of SC with two different competing magnetic instabilities is proposed.
[1] G. Fuchs, S.-L. Drechsler, N. Kozlova et al., PRL 101 in press