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

• Main Authors: Goltz, Til, Zinth, Veronika, Johrendt, Dirk, Rosner, Helge, Pascua, Gwendolyne, Luetkens, Hubertus, Materne, Philipp, Klauss, Hans-Henning
• Format: Journal Article
• Language: English
• Published: 04-02-2014
• Subjects: Physics - Superconductivity
• DOI: 10.48550/arxiv.1402.0711

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, M\"ossbauer 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, M\"ossbauer spectroscopy,
muon spin relaxation and ac susceptibility measurements on polycrystalline
samples is complemented by density functional electronic structure
calculations.