Microscopic Coexistence of Magnetism and Superconductivity in charge compensated Ba1-xKx(Fe1-yCoy)2As2

Abstract

We present a detailed investigation of the electronic phase diagram of effectively 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 \< 0.13, the system displays an orthorhombically distorted and antiferromagnetically ordered ground state. The low temperature structural and magnetic order parameters are successively reduced with increasing substitution level. We observe a linear relationship between the structural and the magnetic order parameter as a function of temperature and substitution level for x/2 = y \< 0.13. 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 higher substitution levels x/2 = y \> 0.25 a tetragonal non-magnetic ground state is observed. Our DFT calculations yield a signifcant reduction of the Fe 3d density of states at the Fermi energy and a strong suppression of the ordered magnetic moment in excellent agreement with experimental results. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to non-magnetic impurities to a system with a constant charge carrier density. 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.

16 pages, 14 figures

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• The phase diagrams of iron-based superconductors: theory and experiments
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• Probing the pairing symmetry in the over-doped Fe-based superconductor Ba_0.35Rb_0.65Fe_2As_2 as a function of hydrostatic pressure
• Disentangling superconducting and magnetic orders in NaFe_1-xNi_xAs using muon spin rotation
• Local spectroscopic evidence for a nodeless magnetic kagome superconductor CeRu${}_2$
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• Superconductivity-induced transverse plasma mode and phonon anomaly in the $c$-axis response of the bilayer compound RbCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Atomic-scale coexistence of short-range magnetic order and superconductivity in Fe${}_{1+y}$Se${}_{0.1}$Te${}_{0.9}$
• Impurity effects on spin dynamics in magnetic and superconducting iron pnictides and chalcogenides
• Mössbauer studies of spin- and charge-modulations in BaFe2(As1-xPx)2
• Microscopic phase diagram of LaFeAsO single crystals under pressure