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TT: Fachverband Tiefe Temperaturen

TT 12: Poster Session Superconductivity

TT 12.37: Poster

Monday, March 11, 2013, 15:00–19:00, Poster D

Specific heat measurements of single-crystalline iron superconductors K_1−xNa_xFe₂As₂ and of Li₂ZrCuO₄ down to 10 mK — •Patrick Vogt¹, Andreas Reifenberger¹, Mahmoud Abdel-Hafiez², Sai Aswartham², Sabine Wurmehl², Marius Hempel¹, Stefan-Ludwig Drechsler², Bernd Büchner², Andreas Fleischmann¹, Christian Enss¹, and Rüdiger Klingeler¹ — ¹Kirchhoff-Institute for Physics, University of Heidelberg, D-69120 Heidelberg, Germany — ²Leibniz-Institute for Solid State and Materials Research, IFW-Dresden, D-01171 Dresden, Germany

Specific heat studies down to very low temperatures are applied to study electronic properties in the superconducting phase of K_1−xNa_xFe₂As₂ and low-energy excitations in the quasi-one-dimensional quantum antiferromagnet Li₂ZrCuO₄. A quasi-adiabatical heat-pulse method including the τ₂-effect yields specific heat data on K_1−xNa_xFe₂As₂ single crystals with different doping levels down to 10 mK. The data show clear evidence for a T²-term in specific heat providing evidence for line nodes in the superconducting order parameter. For insulating Li₂ZrCuO₄, a continuous dual-slope method is applied which implies linearly-in-temperature increasing specific heat below 1 K superimposed by an anomaly centered at 60 mK. The anomalously large slope in the linear regime highlights the relevance of quantum fluctuations of presumably magnetic nature.