Workshop "NMR, µSR, Mössbauer spectroscopies in the study of Fe-based and other unconventional high-Tc superconductors"
Coexistence of Magnetism and Superconductivity in Charge-Compensated Ba1-xKx(Fe1-yCoy)2As2
Hans-Henning Klauß, TU Dresden, Germany
We present a detailed investigation of the electronic phase diagram of nominally charge compensated Ba1−xKx(Fe1−yCoy)2As2 with x/2 ≈ y . Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels of x/2 ≈ y ≤ 0.10, the system displays a BaFe2As2-like antiferromagnetic, orthorhombic ground state with a reduced orthorhombic distortion and ordered magnetic moment. We experimentally observe a linear relationship between the structural and the magnetic order parameter for x/2 ≈ y ≤ 0.13 (see below). At intermediate substitution levels in the range between 0.13 and 0.19, we find superconductivity with a maximum Tc of 15 K coexisting with static magnetic order on a microscopic length scale. For x/2 ≈ y ≥ 0.25, we find a tetragonal, non magnetic ground state. Our DFT calculations yield a strong suppression of the ordered magnetic moment in excellent agreement with experimental results.
The obtained electronic phase diagram of Ba1-xKx(Fe1-yCoy)2As2 (see above) is being discussed in the context of disorder due to non-magnetic impurities in a system with a constant charge carrier density  and preemptive nematic order in the iron pnictides .
 T. Goltz et al., arXiv:1402.0711 (2014)
 M. Vavilov, A. V. Chubukov, Phys. Rev. B 84, 214521 (2011)
 R. M. Fernandes et al., Phys. Rev. B 85, 024534 (2012)