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The fluctuating hydrogen bridge bonded network of liquid water at ambient conditions entails a varied ensemble of the underlying constituting H2O molecular moieties. This is mirrored in a manifold of the H2O molecular potentials. Subnatural line width resonant inelastic X-ray scattering allowed us to quantify the manifold of molecular potential energy surfaces along the H2O symmetric normal mode and the local asymmetric O–H bond coordinate up to 1 and 1.5 Å, respectively. The comparison of the single H2O molecular potentials and spectroscopic signatures with the ambient conditions liquid phase H2O molecular potentials is done on various levels. In the gas phase, first principles, Morse potentials, and stepwise harmonic potential reconstruction have been employed and benchmarked. In the liquid phase the determination of the potential energy manifold along the local asymmetric O–H bond coordinate from resonant inelastic X-ray scattering via the bound state oxygen 1s to 4a1 resonance is treated within these frameworks. The potential energy surface manifold along the symmetric stretch from resonant inelastic X-ray scattering via the oxygen 1s to 2b2 resonance is based on stepwise harmonic reconstruction. We find in liquid water at ambient conditions H2O molecular potentials ranging from the weak interaction limit to strongly distorted potentials which are put into perspective to established parameters, i.e., intermolecular O–H, H–H, and O–O correlation lengths from neutron scattering. [ABSTRACT FROM AUTHOR]

The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 ± 2.1% donated and accepted hydrogen bonds per molecule, pointing to a continuousdistribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray-matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscalelength correlations within the continuous distribution remains open. [ABSTRACT FROM AUTHOR]

Vortex dynamics in a multiband anisotropic superconductor, such as the Fe based superconductors, is interesting and potentially important for applications. In this study we examine flux-creep data for fields along the second magnetization peak observed in M(H) curves of BaFe1.9Ni0.1As2 for H k c-axis, H k ab-planes and H forming a 45° angle with ab-planes. We find that the M-H loops taken from the different field directions can be collapsed onto a single universal curve at all temperatures with a simple scaling factor equivalent to the superconducting anisotropy, showing that the vortex pinning is not only isotropic and three-dimensional but most likely related to point-like defects. The resulting critical currents, however, taken from the Bean model appear to show enhanced low field pinning for H k c. The features in the vortex dynamics also differ in different field orientations and show no direct correlation with the second magnetization peak Hp as is the case with a direct crossover in pinning regimes. Isofield plots of the scaled activation energy obtained from flux-creep data are found to be a smooth function of temperature as the Hp(T) line is crossed, consistent with a single type of pinning regime operating at this field, independent of field orientation. The functional form of the Hp(T) lines in the resulting phase diagrams also support this view. [ABSTRACT FROM AUTHOR]

We study the diamagnetism induced by thermal fluctuations above the superconducting transition of the iron pnictide Ba(FeNix)2As2 with different doping levels. The measurements are performed with magnetic fields up to 7 T applied in the two main crystal directions. These data provide double information: first, they confirm at a quantitative level the applicability to these materials of a 3D-anisotropic Ginzburg–Landau approach valid in the finite field regime. Then, they allow us to determine the doping-level dependence of the in-plane coherence length and of the superconducting anisotropy factor, γ. Our results provide a stringent confirmation of the large increase of γ with the doping level, as recently proposed from magnetoresistivity measurements. The implications of the applicability of the model used to a multiband superconductor are discussed. [ABSTRACT FROM AUTHOR]

We use transport and magnetization measurements to study the effect of Cr-doping to the phase diagram of the electron-doped superconducting BaFe2−xNixAs2 iron pnictides. In principle, adding Cr to electron-doped BaFe2−xNixAs2 should be equivalent to the effect of hole-doping. However, we find that Cr doping suppresses superconductivity via impurity effect, while not affecting the normal state resistivity above 100 K. We establish the phase diagram of Cr-doped BaFeNixCryAs2 iron pnictides, and demonstrate that Cr-doping near optimal superconductivity restore the long-range antiferromagnetic order suppressed by superconductivity. [ABSTRACT FROM AUTHOR]