Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 30: Superconductivity - Poster Session

TT 30.38: Poster

Monday, March 31, 2014, 15:00–19:00, P2

Low-temperature specific heat of K_0.71Na_0.29Fe₂As₂ down to 20 mK — •Andreas Reifenberger, Marius Hempel, Andreas Fleischmann, Ruediger Klingeler, and Christian Enss — Kirchhoff-Institut für Physik, Universität Heidelberg, INF 227, D-69120 Heidelberg

Specific heat measurements on K_1−xNa_xFe₂As₂ at very low temperatures are helpful for the understanding of the underlying symmetry and magnitude of the superconducting order parameter. To perform the measurements, we used a commercially available calorimeter which we calibrated in the temperature range 0.02   K ≤ T ≤ 0.8   K. The data on K_0.71Na_0.29Fe₂As₂ imply the presence of a large T² contribution to the specific heat which gives evidence of d-wave symmetry of the superconducting order parameter on almost all Fermi-surface sheets. To extend these measurements to even lower temperatures, we have designed a novel calorimeter based on magnetic thermometry. We expect a temperature resolution Δ T ≈ 0.1   µ K and an addenda heat capacity of less than 200   pJ/K for T < 100   mK.