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TT: Fachverband Tiefe Temperaturen
TT 34: SC: Iron-Based Superconductors - 122
TT 34.12: Talk
Thursday, March 25, 2010, 17:00–17:15, H20
Point-contact spectroscopy on doped and undoped 122 barium iron pnictides in the normal-conducting state — •Oliver Berg1, Michael Marz1, Thomas Wolf2, Hilbert v. Löhneysen1,2, and Gernot Goll1 — 1Physikalisches Institut, Karlsruher Institut für Technologie, 76131 Karlsruhe — 2Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
Point-contact spectroscopy (PCS) measurements in the superconducting state of K- and Co-doped BaFe2As2 single crystals exhibit, in addition to features due to superconductivity, an unexpected, weakly temperature-dependent voltage-dependence of the differential conductance dI/dV in both the superconducting and in normal states. To clarify the origin of this behavior we have investigated PCS of doped and undoped Ba-122 single crystals up to T=200 K. In additon to this ubiquitous voltage dependence, undoped BaFe2As2 crystals reveal a significant zero anomaly (ZBA) of the differential conductance that is common to antiferromagnetic materials. Our observation that the ZBA is absent in the doped, i. e., superconducting samples supports this assignment because doping of BaFe2As2 with K or Co is known to suppress the antiferromagnetic ordering. The spectra can be described with two Lorentzian functions for the the different contributions. These doped samples (Ba0.68K0.32Fe2As2 and Ba(Fe0.935Co0.065)2As2) exhbit at T < Tc the dI/dV spectra expected of Andreev reflection for two-band superconductors.