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TT: Fachverband Tiefe Temperaturen

TT 49: Poster Session: Superconductivity

TT 49.16: Poster

Mittwoch, 3. April 2019, 15:00–18:30, Poster D

NMR investigations of the iron-pnictide superconductor KFe₂As₂ near the upper critical field — •Sh. Yamamoto¹, S. Molatta¹, F. Hardy², R. Lortz³, J. Wosnitza¹, and H. Kühne¹ — ¹Hochfeld-Magnetlabor Dresden (HLD-EMFL), HZDR, Dresden, Germany — ²Institute for Solid State Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany — ³Department of Physics, The Hong Kong University of Science and Technology, Kowloon, Hong Kong

Recent measurements by thermodynamic probes provided evidence for a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in the iron-pnictide superconductor KFe₂As₂ beyond the Pauli limit for in-plane applied fields. We report two aspects of the ⁷⁵As nuclear magnetic resonance in KFe₂As₂ near the upper critical field (H_c2). First, according to the angular and temperature dependence of spin-echo measurements, no observable line broadening above the Pauli limit was observed for a high-quality single crystal. The result gives a spectroscopic viewpoint on the proposed FFLO state. Second, we observed an angle-independent line broadening of the central and the satellite peak below 500 mK near H_c2. Furthermore, two distinct nuclear spin-lattice relaxation times were observed at low temperatures. These results are compatible with the existence of charge order or charge fluctuations that has been, so far, only observed under pressure (KFe₂As₂) or in zero field (RbFe₂As₂) in strongly hole-doped 122 iron-based superconductors.