Dresden 2014 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 53: Superconductivity: Fe-based Superconductors - 122
TT 53.5: Talk
Wednesday, April 2, 2014, 10:30–10:45, HSZ 201
Specific heat of Ca0.32Na0.68Fe2As2 single crystals: unconventional s± multi-band superconductivity with intermediate repulsive interband coupling and sizable attractive intraband couplings — •S.-L. Drechsler1, S. Johnston1, H. Rosner2, M. Abdel-Hafiez1, V. Grinenko1, L. Harnagea1, Y. Krupskaya1, D. Bombor1, S. Wurmehl1, C. Hess1, A. Wolter1, and B. Buechner1 — 1IFW-Dresden, Germany — 2MPI CPfS-Dresden, Germany
We report a low-temperature specific heat study of single crystals of the heavily hole doped superconductor Ca0.32Na0.68Fe2As2. This compound exhibits bulk superconductivity with a transition temperature Tc ≈34 K, which is evident from the magnetization, transport, and specific heat measurements. The zero field data manifests a significant electronic specific heat in the normal state with a Sommerfeld coefficient γ ≈53 mJ/mol K2. Using a multi-band Eliashberg analysis, we demonstrate that the dependence of the zero field specific heat in the superconducting state is well described by a three-band model with an unconventional s± pairing symmetry and gap magnitudes Δi of about 2.35, 7.48, and -7.50 meV. Our analysis indicates a non-negligible attractive intraband coupling,which contributes significantly to the relatively high value of Tc. The Fermi surface averaged repulsive and attractive coupling strengths are of comparable size and outside the strong coupling limit frequently adopted for describing high-Tc iron pnictide superconductors. We further infer a total mass renormalization of the order of five, including the effects of correlations and electron-boson interactions.