In-plane electronic anisotropy of differently doped AFe2As2 (A = Ba, Eu) superconductors

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Single crystals of AFe2As2 (A=Ca, Ba, Eu) based materials and related transition metal pnictides will be synthesized, in which the strength of electronic correlations and the ground state is tuned. Specifically, we compare the effects of hole doping in Eu1-x KxFe2As2 with hydrostatic as well as chemical pressure in EuFe2(As1-xPx)2 with particular emphasis on the magnetic quantum phase transition, the emergence of superconductivity and its interplay with Eu2+ local moments. In hydrostatically or chemically pressurized EuFe2As2, the ordering of Eu-moments below 20 K leads to distinct anomalies in the superconducting properties. Additionally, in order to classify the strength of electronic correlations of iron-arsenites with respect to the cuprates and other unconventional superconductors, negative chemical pressure is applied in (Ca,Ba)Fe2(As1-xSbx)2 to tune the system towards the stronger correlated state. Furthermore, the isostructural small-bandgap insulator and antiferromagnet BaMn2As2 is tuned towards the metallic state by hole doping. Our single crystals are investigated by transport, magnetic and thermodynamic probes, as well as within collaborations by optical- and far-infrared spectroscopy, angular-resolved photo-emission spectroscopy, electron-spin resonance and further techniques.