Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 45: Superconductivity: Ferropnictides 2

TT 45.5: Vortrag

Freitag, 27. März 2009, 11:30–11:45, HSZ 03

Probing the superconductive energy gap of the iron pnictide superconductor Ba_1−xK_xFe₂As₂ by point-contact and scanning tunnelling spectroscopy — •Gernot Goll¹, Michael Marz¹, Samuel Bouvron¹, Tihomir Tomanic¹, Veronika Fritsch¹, Hilbert v. Löhneysen^1,2, and Thomas Wolf² — ¹Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe, Germany — ²Institut für Festkörperphysik, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany

The size of the superconductive energy gap and its directional dependence is one of the central issues of studies on the recently discovered iron pnictide superconductors. The knowledge of both properties is essential for the characterization and a closer understanding of the mechanism of superconductivity. We report on point-contact measurements on (Ba,K)Fe₂As₂/Pt point contacts. (Ba,K)Fe₂As₂ single crystals were prepared by the flux-growth technique with Sn flux. Superconductivity was probed by resistivity and magnetization measurements. A superconducting transition temperature T_c^50% = 26.5 K was found resistively for x=0.28. Andreev reflection of charge carriers at the superconductor/normal metal interface of Ba_0.72K_0.28Fe₂As₂/Pt point contacts was utilized to determine the energy gap for current flow parallel and perpendicular to the FeAs planes. In first measurements, with current flow within the plane, the diffential conductance versus voltage curves reveal a multi-gap nature of the superconductive order parameter with a small gap of about 3 meV and a larger one with 7-8 meV.