## Workshop "NMR, µSR, Mössbauer spectroscopies in the study of Fe-based and other unconventional high-*T*_{c} superconductors"

_{c}

__Coexistence of Magnetism and Superconductivity in Charge-Compensated Ba _{1-}_{x}K_{x}(Fe_{1-y}Co_{y})_{2}As_{2}__

Hans-Henning Klauß, TU Dresden, Germany

We present a detailed investigation of the electronic phase diagram of nominally charge compensated Ba_{1−x}K_{x}(Fe_{1−y}Co_{y})_{2}As_{2} with *x*/2 ≈ *y* [1]. 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 BaFe_{2}As_{2}-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 *T _{c}* 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 Ba_{}_{1-x}K* _{x}*(Fe

_{1-}

*Co*

_{y}*)*

_{y}_{2}As

_{2}(see above) is being discussed in the context of disorder due to non-magnetic impurities in a system with a constant charge carrier density [2] and preemptive nematic order in the iron pnictides [3].

[1] T. Goltz et al., *arXiv:*1402.0711 (2014)

[2] M. Vavilov, A. V. Chubukov, *Phys. Rev. B* **84**, 214521 (2011)

[3] R. M. Fernandes et al., *Phys. Rev. B* **85**, 024534 (2012)