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TT: Fachverband Tiefe Temperaturen

TT 31: Superconductivity: Fe-based Superconductors – 122 and 111

TT 31.1: Topical Talk

Dienstag, 17. März 2015, 09:30–10:00, H 2053

Electronic Correlations in Hole- and Electron-Doped Fe-Based Superconductors and Evidence for the C₄-Magnetic Phase in Ba_1−xK_xFe₂As₂ — •Frédéric Hardy¹, Anna Böhmer¹, Thomas Wolf¹, Peter Schweiss¹, Rolf Heid¹, Robert Eder¹, Robert A. Fisher², and Christoph Meingast¹ — ¹IFP, Karlsruhe Institute of Technology, Karlsruhe, Germany — ²Lawrence Berkeley National Laboratory, Berkeley CA, USA

High-T_c superconductivity in the cuprates occurs at the crossover from a correlated Mott insulating state to a weaker correlated Fermi liquid as a function of doping. The Fe-pnictides were initially thought to be weakly correlated. However, we have recently shown that KFe₂As₂ is in fact highly correlated. These correlations are even further enhanced in Rb- and CsFe₂As₂. The temperature dependence of both the susceptibility and the thermal expansion provides strong evidence for the existence of a coherence-incoherence crossover. Whereas the correlations in the cuprates result from a large value of the Hubbard U, recent works have stressed the particular relevance of Hund’s coupling J in the pnictides. Our data may be interpreted in terms of a close proximity to an orbital-selective Mott transition. We now have good thermodynamic data covering both the hole and electron doping sides of the BaFe₂As₂ system and we will discuss how these correlations are modified by doping. We have also re-examined in detail the underdoped region of Ba_1−xK_xFe₂As₂. We find a small region of C₄ symmetry inside the SDW state similar to that of Na_1−xBa_xFe₂As₂. We will show how this new phase interacts with both superconductivity and SDW.