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TT: Fachverband Tiefe Temperaturen

TT 13: Superconductivity: Fe-based Superconductors - 122

TT 13.10: Vortrag

Montag, 20. März 2017, 17:30–17:45, HSZ 103

Quantum criticality in AFe₂As₂ (A = K, Rb, Cs) superconductors probed by ⁷⁵As NMR spectroscopy — Z.T. Zhang^1,2, D. Dmytriieva^1,3, S. Molatta^1,3, J. Wosnitza^1,3, S. Khim⁴, S. Gass⁴, A.U.B. Wolter-Giraud⁴, S. Wurmehl⁴, H.-J. Grafe⁴, and •H. Kühne¹ — ¹Hochfeld-Magnetlabor Dresden, Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden — ²Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China — ³Institut für Festkörperphysik, TU Dresden, 01060 Dresden — ⁴IFW Dresden, Institute for Solid State Research, 01171 Dresden

We present ⁷⁵As nuclear magnetic resonance measurements on single crystals of RbFe₂As₂ and CsFe₂As₂. Taking previously reported results for KFe₂As₂ into account, we find that the anisotropic electronic correlations evolve towards a magnetic instability in the AFe₂As₂ series (with A = K, Rb, Cs). Upon isovalent substitution with larger alkali ions, a drastic enhancement of the anisotropic nuclear spin-lattice relaxation rate and decreasing Knight shift reveal the formation of pronounced spin fluctuations with stripe-type modulation. Furthermore, a decreasing power-law exponent of the nuclear spin-lattice relaxation rate for in-plane applied fields evidences an emergent deviation from Fermi-liquid behavior. All these findings clearly indicate that the expansion of the lattice in the AFe₂As₂ series tunes the electronic correlations towards a quantum critical point at the transition to a yet unobserved, magnetically ordered phase.