The role of different negatively charged layers in Ca 10 (Fe 1−x Pt x As) 10 (Pt The recently discovered compounds Ca10(Fe1−xPtxAs)10(Pt3+yAs8) exhibit superconductivity up to 38 K, and contain iron arsenide (FeAs) and platinum arsenide (Pt3+yAs8) layers separated by layers of Ca atoms. We show that high Tc's above 15 K only emerge if the iron-arsenide layers are at most free of platinum-substitution (x → 0) in contrast to recent reports. In fact Pt-substitution is detrimental to higher Tc, which increases up to 38 K only by charge doping of pure FeAs layers. We point out, that two different negatively charged layers [(FeAs)10] n− and (Pt3+yAs8) m− compete for the electrons provided by the Ca 2+ -ions, which is unique in the field of iron-based superconductors. In the parent compound Ca10(FeAs)10(Pt3As8), no excess charge dopes the FeAs-layer, and superconductivity has to be induced by Pt-substitution, albeit below 15 K. In contrast, the additional Pt-atom in the Pt4As8 layer shifts the charge balance between the layers equivalent to charge doping by 0.2 electrons per FeAs. Only in this case Tc raises to 38 K, but decreases again if additionally platinum is substituted for iron. This charge doping scenario is supported by our discovery of superconductivity at 30 K in the electron-doped La-1038 compound (Ca0.8La0.2)10(FeAs)10(Pt3As8) without significant Pt-substitution.

Superconductivity by rare earth doping in the 1038-type compounds ðCa 1 À x RE x Þ 10 ðFeAsÞ 10 ðPt 3 As 8 Þ with RE¼ Y, a b s t r a c t We report superconductivity in polycrystalline samples of the 1038-type compounds ðCa 1 À x RE x Þ 10 ðFeAsÞ 10 ðPt 3 As 8 Þ up to T c ¼ 35 K with RE¼ Y, La-Nd, Sm, Gd-Lu. The critical temperatures are nearly independent of the trivalent rare earth element used, yielding a common T c ðx RE Þ phase diagram for electron doping in all these systems. The absence of superconductivity in Eu 2 þ doped samples, as well as the close resemblance of ðCa 1 À x RE x Þ 10 ðFeAsÞ 10 ðPt 3 As 8 Þ to the 1048 compound substantiate that the electron doping scenario in the RE-1038 and 1048 phases is analogous to other iron-based superconductors with simpler crystal structures.

The angle-resolved photoemission spectra of the superconductor (Ba1−xKx)Fe2As2 have been investigated accounting coherently for spin-orbit coupling, disorder and electron correlation effects in the valence bands combined with final state, matrix element and surface effects. Our results explain the previously obscured origins of all salient features of the ARPES response of this paradigm pnictide compound and reveal the origin of the Lifshitz transition. Comparison of calculated ARPES spectra with the underlying DMFT band structure shows an important impact of final state effects, which result for three-dimensional states in a deviation of the ARPES spectra from the true spectral function. In particular, the apparent effective mass enhancement seen in the ARPES response is not an entirely intrinsic property of the quasiparticle valence bands but may have a significant extrinsic contribution from the photoemission process and thus differ from its true value. Because this effect is more pronounced for low photoexcitation energies, soft-X-ray ARPES delivers more accurate values of the mass enhancement due to a sharp definition of the 3D electron momentum. To demonstrate this effect in addition to the theoretical study, we show here new state of the art soft-X-ray and polarisation dependent ARPES measurments.

We present a comprehensive study on the low-temperature orthorhombic phase of Ba(Fe 1-x Co x ) 2 As 2 based on the Korringa-Kohn-Rostoker-Green function approach. Using this bandstructure method in combination with the coherent potential approximation alloy theory we are able to investigate the evolution of the magnetic and electronic properties of this prototype iron pnictide for arbitrary concentrations x, while dealing with the chemical disorder without uncontrolled simplifications by using solely a rigid band shift or the virtual crystal approximation. We discuss the development of the site resolved magnetic moments for the experimentally observed stripe antiferromagnetic order together with the strong electronic anisotropy of the Fermi surface and compare it with angle-resolved photoemission spectroscopy measurements of detwinned crystals. We furthermore calculate magnetic exchange coupling parameters Jij and use them for Monte-Carlo simulations on the basis of the classical Heisenberg model to get an insight on the temperature dependence of the magnetic ordering on the cobalt concentration.

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An innovative integrated sensing platform for the detection of various chemical analytes via translating the photonic stop-band shift of a one-dimensional photonic crystal (PC) into an electrical current change is proposed. The miniaturized sensing platform features an organic light-emitting diode (OLED) as a light source and an organic photodetector (OPD) as a light sensor and allows for the detection of ethanol vapor concentrations down to 10 parts per million (ppm) in nitrogen, which corresponds to a stop-band shift of 27 pm. The resolution of the proposed platform exceeds the capabilities of most commercial spectrometers and by far the human eye, while, at the same time, such a sensor is less expensive and less power consuming than a spectrometer. The presented setup is generic and can detect optical changes in the transmission of PCs, which can be induced by both vapor adsorption or by a liquid analyte, as demonstrated with a microfluidic setup.

The hyperfine field B hf and the magnetic properties of the BaFe2As2 family are studied using the fully relativistic Dirac formalism for different types of substitution. The study covers electron doped Ba(Fe1−xCox)2As2 and Ba(Fe1−xNix)2As2, hole doped (Ba1−xKx)Fe2As2 and also isovalently doped Ba(Fe1−xRux)2As2 and BaFe2(As1−xPx)2 for a wide range of the concentration x. For the substituted compounds the hyperfine fields show a very strong dependence on the dopant type and its concentration x. Relativistic contributions were found to have a significantly stronger impact for the iron pnictides when compared to bulk Fe. As an important finding, we demonstrate that it is not sensible to relate the hyperfine field B hf to the average magnetic moment µ of the compound, as it was done in earlier literature.