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TT: Fachverband Tiefe Temperaturen

TT 53: Superconductivity: Fe-based Superconductors - 122

TT 53.5: Vortrag

Mittwoch, 2. April 2014, 10:30–10:45, HSZ 201

Specific heat of Ca_0.32Na_0.68Fe₂As₂ 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 Ca_0.32Na_0.68Fe₂As₂. This compound exhibits bulk superconductivity with a transition temperature T_c ≈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 Δ_i 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 T_c. The Fermi surface averaged repulsive and attractive coupling strengths are of comparable size and outside the strong coupling limit frequently adopted for describing high-T_c iron pnictide superconductors. We further infer a total mass renormalization of the order of five, including the effects of correlations and electron-boson interactions.