Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 27: Superconductivity: Fe-based Superconductors - 122

TT 27.8: Talk

Tuesday, March 12, 2013, 11:45–12:00, H18

Pressure dependencies and first-order transition in KFe₂As₂ — •Philipp Burger^1,2, Anna Böhmer^1,2, Frédéric Hardy¹, Thomas Wolf¹, Peter Schweiss¹, Rainer Fromknecht¹, and Christoph Meingast¹ — ¹Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany — ²Fakultät für Physik, Karlsruher Institut für Technologie, 76128 Karlsruhe, Germany

Here we present a thermodynamic study on KFe₂As₂ single crystals (T_c=3.4 K) using high-resolution thermal-expansion, specific heat, magnetostriction and magnetization measurements. From these measurements we extract the uniaxial pressure dependencies of the Sommerfeld coefficient γ, the critical temperature T_c, the upper critical field H_c2, the magnetic susceptibility χ and the thermodynamical critical field H_c. Interestingly, the normalized pressure derivatives of T_c and H_c are about a factor of 10 larger than the pressure dependence of gamma, clearly showing that T_c is not closely correlated with γ. In particular the pressure dependencies of T_c show a very anisotropic behavior for the two different directions. Similar anisotropic behavior is also observed for H_c2 and H_c indicating that they are strongly coupled to each other.

In addition, magnetostriction and magnetization data for H parallel a-axis show that the superconducting transition is changing from second-order to first-order around 2 K. These results support that the upper critical field H_c2 is strongly suppressed via Pauli paramagnetism.